I got X-COM UFO Defense in a recent Steam sale. Kind of always wanted to play it because I like strategy games and heard this one was awesome. I just started up a game for the first time... and have no idea where to even start. The game gives absolutely zero guidance- it jumps dumps you onto a world map and say "Go". So my questions is: How dense is this game? Will I have to do something along the lines of find a manual and read for hours just to understand basic gameplay mechanics? Once I've learned the basics, how long does a full game take? Any guidance would be appreciated. The game at least isn't intent on giving me any.

Every game on Steam has a manual on the store page.

I haven't played this game in about 13 years, I do remember having to resort to the manual often though.

Ok, X-Com is basically you're in charge of a highly secretive army created from all of Earth's governments collaborating together to stop an alien invasion. You ultimately have to retro-engineer their technology, and put a stop to their threat by finding out where they're coming from.
 
You have to protect your countries from alien infiltration, otherwise they will turn those countries and they'll stop funding you, and you need funding. At the same time you need alien tech to sell and research to find out their motives.
 
You start off with a base on the geoscape, it's that blue square. I'd recommend putting your base in the highest North Africa, the Germany/France border or America, for they fund the most/you have protective range over high funding countries. Clicking Bases will give you an overview of the insides of your bases where you can add facilities, labs allow for more scientist stuff, etc while workshops allow engineering. The UFOPeadia has more information on what each base installation does, Alien Containment is also needed to capture live aliens so I recommend getting that at the start. Inside Bases there's a Research tab which you use to research stuff you capture. You also have 3 "earth" techs, Lasers, Medi-Kits and Scanners, go for the Medi-Kits first and assign your scientists to that, you'll need them.

You have a time system, research is done over hours/days, and so too do the aliens and your/their movement. Check the Graphs to find out where they're at and what countries are reporting alien activity. When a UFO is detected, it appears as a red cross. Send your Interceptors from the Intercept button and click on the red cross, and they will chase after it. If you manage to get to it, shoot it down with Aggressive Attack (it's the only decent one all the time unless you have some special weapon configurations). Either you 1) shoot it down 2) it runs away and your Interceptors must keep pursuing 3) you flee or 4) you get shot down. More often 1) or 2) at this point as they're small fries at the start. When you shoot them down, they appear as a white "X", send a Skyranger from Intercept to it to do a ground assault TBS. The aliens can also appear as a green "X"- this means they have landed and are doing their "missions". You'll want to ground assault them if you feel up to it, but be advised that the UFO there is intact but they have a full alien crew complement so it can be a two edged sword.
 
You also must buy soldiers, equipment for them, tanks and such and watch them grow in status/experience. At the start they suck but they will persist if you use things such as cover and play soldiers to their advantages (veterans in the back, rookies in the front, smoke grenades, etc). Then you just assign them/the equipment to a Skyranger.
 
Eventually the aliens will send terror attacks and ships to cities, you don't want to ignore them otherwise this will put your score in so much dirt you'll be on the road to losing X-Com. Aliens will also set up bases over time, these generate in their areas a heck of a lot of alien activity.
 
If you're doing too well, the aliens might attack your base. If you lose your last base (which is often your first), you lose and doom Earth to the aliens, it's simple. Other ways of losing are:
Failing the final mission.
Being in serious debt for two consecutive months so you get shut down.
Having a poor score for two consecutive months.
 
Score is calculated by your activities (successful missions, shot down UFOs) minus the aliens activities (abduction, infiltration, terror, etc).

• First off, start your main base in Europe or East Asia. Those two areas have the most coverage as far as landmass goes, although you could probably get away with having one in Central America as well. 
• On the management side build two hangars next to the one on top and, once they are built get rid of the ones on bottom. Why? Because if aliens retaliate then they will only be able to come down from one direction. Alternatively, you could set up a second base somewhere else to maximize coverage, although that would probably stretch funds pretty thin. In reality, Aliens will always appear around your first base for at least a month.
• Also build a long range radar and Alien Containment. But that's fairly obvious.
• Now, look through all your squaddies. Keep the ones that have Marksmanship over 50, and especially keep the ones with reactions over 50, as those guys will be your scout types. High action points and strength are also a plus. Health really doesn't matter at this point, since everyone on your squad will die in one shot 99% of the time anyways. Ditch the rest.
  
• Now, what I like to do is designate roles for my guys, not that I especially keep to them. This I achieve by adding a letter to the end of the character's name. So SN for snipers with high accuracy but perhaps not the best reactions, G for general, GN for Grenadiers, SC for scouts with high reactions stats, HW for heavy weapons guys with strength stats around 30. Eventually I also add PSI for guys with high psionic stats, and MD for people with medkits. It also helps as a way to figure out who to ditch when you get to that screen.
• Equipment wise, you probably can get away with getting rid of pistols, which are rather worthless anyways. You can maybe get rid of heavy cannons, but I still think they have their merits when compared with auto cannons. In any case, also get rid of cannons for your interceptors, because they suck, and focus entirely on stingray and avalanche missiles. Otherwise, stick to rifles for most of your guys, except for those who are strong enough to use cannons and Rocket Launchers.
• HWP tanks are worth using as both scouts, but the Rocket Launcher varieties are better than the cannon ones because of their ability to cause widespread destruction.
  
• Research Laser Weapons ASAP. They are significantly better than the stuff you start with. Also research Alien Alloys --> Personal Armor. It improves the survivability of your dudes by quite a bit. I think that 20-30 scientists is a good number to start with.
  
• Buy some proximity grenades, electro-flares for night missions, and stun rods. Because you can, and because stun rods are the only way to reliably capture aliens in the early game. But don't bother using them until you get Alien Containment built.
  
• As for the missions themselves? Try not do do them at night. Shot down UFOs linger for a while, so you can wait. Touched down UFOs (in green) are more valuable because they have fuel but also have more enemies.  Terror missions at night are pretty much the worst things ever, but avoid one too many and you will be screwed over in the funding department.
  
• Have your dudes with high reactions (scouts) enter the UFO. Set it so you have enough action points left for a reaction shot, which is quite helpful.
  
• Expect for people to die. It's inevitable. If someone with high stats or otherwise high importance dies, restart. But you can save mid-battle, so it's not a huge issue.
  

You are on your own from this point, although there are videos on Youtube that also are pretty helpful. I hope my long list of bullets helps!

" Every game on Steam has a manual on the store page. "

Thanks for all the pointers everyone. I at least have a starting point now :)

@ArbitraryWater:

Hey, with the news about a new Firaxis X-Com game, I've been playing the original game, and after "trying" to play for a while I find your tips to be pure gold. Just a few questions tho:

• You said Pistols are pretty much worthless, but in practice like 80% of the kills I get have been with pistols, specially at "long" range. Am I doing something wrong with the rifles? I seem to miss every time, with my high accuracy dudes even. Is there a way to calculate the optimal range for all weapons?
• Leaving some Time Points left for reaction shots changed the whole game, holy crap, I had no idea how important that was. But I notice you can leave enough TP for a snap shot, a burst shot or an aimed shot. Which should I aim to leave time points for? I've been doing just snap shots, but I dunno.
• I tried doing one of those terror missions, holy shit! They keep mind-controlling my heavy, and asploding like 5 guys with one shot, and then everyone goes bananas after that. I can't figure out how to approach those missions. I read somewhere that you can research anti mind-control stuff. I guess I should put off doing terror missions until I get that? Or is it a stats thing and I shouldn't take weak-minded dudes at all?

Thanks duder!

@Informant said:

veterans in the back, rookies in the front, smoke grenades, etc

I can't figure out when to use smoke granades. I was approaching it as Counter Strike, throwing them in a room before storming in. But they can still shoot you as reaction, and then the smoke will stay there so you'll be at a shooting disadvantage as well, I think? any tips on its usage would be greatly appreciated.

@Dredlockz said:

@ArbitraryWater:

Hey, with the news about a new Firaxis X-Com game, I've been playing the original game, and after "trying" to play for a while I find your tips to be pure gold. Just a few questions tho:

• You said Pistols are pretty much worthless, but in practice like 80% of the kills I get have been with pistols, specially at "long" range. Am I doing something wrong with the rifles? I seem to miss every time, with my high accuracy dudes even. Is there a way to calculate the optimal range for all weapons?
• Leaving some Time Points left for reaction shots changed the whole game, holy crap, I had no idea how important that was. But I notice you can leave enough TP for a snap shot, a burst shot or an aimed shot. Which should I aim to leave time points for? I've been doing just snap shots, but I dunno.
• I tried doing one of those terror missions, holy shit! They keep mind-controlling my heavy, and asploding like 5 guys with one shot, and then everyone goes bananas after that. I can't figure out how to approach those missions. I read somewhere that you can research anti mind-control stuff. I guess I should put off doing terror missions until I get that? Or is it a stats thing and I shouldn't take weak-minded dudes at all?

Thanks duder!

Dont bother with AP cannon FAR TOO SLOW! even thou you need it to take down the Saucers (its an enemy with the sectoids in terror missions) best thing is not to do a a terror mission. The game can give you 5 in a ingame week and have the governments hate you. Or luck out and get 0. So just focus on the ships and get some tech behind you. If you can research Plasma rifles or eve heavy plasma DO IT! Upgrades guns and keep the cannon fodders (soldiers) flowing so you can get tech and build up that way.

Ofcourse the game can just say F U! and throw floaters at you the first mission......that was scarey. First mission in a new game one man scout craft landed. I get shot from the sky there isnt any building...my guy seems him. bastard took out 4 before going down.