Customization

Customization is now a huge part in giving games some depth, allowing the player to change their weapons, armor, vehicles, etc. to whatever they see fit. This also allows the player to make a playing style that fits them and is unique. While there are many different ways you can customize things, they all generally have the same kinds of choices you have in other games.

Guns

Guns are now usually customizable in most shooter games. You usually have many different choices of which to choose from when you are picking your gun and how to best suit it to your death dealing needs. 

Silencers

Silencers are found in many shooting games and are used to muffle the noise made by the gunshots. Silencers are generally used on missions that require stealth, or just make things easier by not alerting every guard in the building of your position. Now this doesn't mean that your shots are completely silent. In most games, if you shoot at someone with a silenced weapon and miss, that person is going to realize somethings up, and be extra cautious. Silencers are great in this regard, however in most games silencers will reduce the accuracy of your weapon, so if the enemy knows of your position, then fire away without the silencer since the chances of your bullet killing the guy shooting at you increase.

Scopes

Scopes are attachments to projectile weapons that are extremely useful when firing at targets from medium-long range. Scopes are great in the way that you can use them to look farther away and see if any 

enemies are in range, and what you are up against. When you have sniper rifles you generally have to hold in your breath to steady the gun. This is one disadvantage of some of the higher magnification scopes since you are firing from a long distance, you have to be very steady otherwise your shot will be wasted and the enemy will know someone is trying to blow their head off. High magnification scopes are also bad when you are facing an enemy at close range since you can't see very well when things are super close to you. This is where red dot scopes come in handy for short range conflicts since it doesn't zoom up but allows you to accurately tell where your bullet is going to land.

Grenade Launchers

Grenade launchers can be found on different assault rifles like the M16 to combat against vehicles or tight groups of enemies. Grenade launchers are very effective at taking out things like light armored vehicles since they move fast and can travel relatively far. Grenade launchers are also effective at stopping enemies who group up. Grenade launchers are effective in that regard, however they are not as effective in close quarters combat since the explosion will damage both your enemy and you. Grenade launcher attachments are also generally single shot so if you miss you have to wait to reload.

Armor

Camouflage

Camouflage is used on both weapons and armor used to make yourself unseen by enemies. It essentially makes you blend in with the environment around you so while you aren't completely invisible, you are close to it. Camouflage is effective when used properly. For example, if you are wearing a ghillie suit in a a grassy hillside, then you are going to be pretty much undetectable, but if you are wearing it while you are breaching a house, you are obviously very noticeable.

Armor Type (Heavy/Light)

Light armor is common in many games whether it be RPG, shooter, action, whatever. Light armor is generally made out of different things depending on the type of game you are playing, or more importantly, what time period the game is set in. If you are in the times of swords, shields, etc. light armor will most likely consist of leather/chain mail. If you are in the present/near-future then you are probably wearing some synthetic armor that doesn't have much stuff on it to weigh you down. The point of light armor is to have some form of protection, while still being relatively quick and agile. You are essentially trading between the weight of the armor with the protection of the armor. Heavy armor is going to be plate armor for games at any time. Not to say they will look exactly the same, but someone wearing heavy armor in say Rainbow Six Vegas 2 are going to be wearing a lot of stuff on them that protects them from enemy fire, but impedes their movement so they can't perform evasive maneuvers effectively. 
 
 
 
 

Units in RTS

Some RTS features customizable units, they give the ability to players to use a chassis, tracks, weapons / tools and such things to make the most versatile unit or the most specific that would fit a certain use
Some other games allow the player to upgrade the units in different ways, this often means that the upgrade have to be made on the units themselves