Fallout 3

Pros

• VATS makes blowing guys up pretty satisfying.

• A bunch of interesting side quests.

• Gets the whole Post Apocalyptic atmosphere down good.

• A larger voice cast in comparison to the three-four people they had for Oblivon.

Cons

• The main quest is extremely short and the conclusion is unsatisfying (though future DLC might rectify that)
• A lot of the humor just fell flat with me.
• Despite the fact you can get companions you never actually feel like you NEED them, the game seems pretty doable solo.
• It's possible through your exploration of the game to drastically screw up the main story line via coming across something you were meant to come across in a later quest.

I'm going to be brief, I hope.
This IS basically Oblivion with guns.
That is NOT a bad thing.
Oblivion was pretty kick ass. Guns add to the kickassedness. A mutant-cyborg shark with laser beam eyes would also help, take note of that for your DLC Bethesda.
Seriously though, it's fine.

You all know the basic story by now.
You're born into a Vault, living solely with your Father after your Mother dropped giving birth to you. All is well and good and then your Dad decides to leave the Vault, which kind of screws things up in a big way for everyone. You of course follow him out into the Wastes and your adventure begins.

Where it begins is really up to you.
You'll be told to head to Megaton to look for information on your father and regardless of whether or not you intend to do that, Megaton is a good place to start - but you don't need to start there. You can pretty much wander where ever you want, which can cause some problems.

When my brother was playing he inadvertently found his Father who went rambling on about Project Purity and Doctor Li and as my brother hadn't touched the main story til now he had no idea what he was rambling about. Of course my brother saved not long beforehand, a bit to late to be able to prevent this from happening, because you tend to naturally assume there would not be something in the game that could screw up the story for you so bad. I guess we were wrong to assume that. You sure showed us, Bethesda!

Combat, much to the dismay of certain Fallout fans - plays out in real time and not entirely unlike a FPS. If it weren't for the addition of VATS I too would be up in arms, but VATS makes me tolerate it. So you have action points like a regular Fallout game, but instead of using them to move, use items, whatever they're used to target specific body parts. But not too specific - unlike previous Fallout games you can't target peoples groins or eyes, but the end result is still often fabulously gory death, which to me at least never gets old.

Some folk insist that VATS makes the game too easy, but without VATS I'm a pretty crappy aim. Play like a shooter it might, but it doesn't play as well as one, free form aiming with my generally crappy FPS skills is difficult. VATS helps ease that somewhat.

In the end, if you came in expecting a traditional Fallout game for some reason you'll likely be disappointed.

If however, the idea of Oblivion with guns works for you or you just need a change of scenery, something different from the Fantasy and Sci Fi most RPGs throw your way, this will work.
Especially if you get the PC version, in which mods might work out a lot of the kinks regardless of what Bethesda winds up doing.