Which Rainbow Six? I have an old one for Play Station 1, Rainbow Six 3 and Rainbow Six 3 Black Arrow for the Xbox. I think I Played Rainbow Six Vegas on the PC, it was one of the newer ones. It didn't feel enough like Rainbow Six for me to continue playing.
I was playing Warrock for the longest time but I couldn't get used to sniping in that game, I had to set my sensitivity so low that I would need a 2 foot mouse pad just to turn 180 degrees without my crosshair jumping 2 to 4 pixels. I think this is due to the lack of mouse acceleration in the game plus having a lower DPI mouse. What I really love about this game is that hit registration is client side for the shooter. If both players shot at the same time, they both died at the same time.
I then jumped to COD MW2 for a while, I think I'm on prestige 5 or 6. I then stopped playing because after playing Counter Strike Source, I realized how shitty the responsiveness of the game is. First of all, the game sends your mouse input to the host, the host then reports back and tells the game to turn your camera so many degrees. You can feel the delay and end up constantly over shooting or under shooting. The second part that made me quit was the extreme bullet delay. It took at least 3/4 a second for the server to register your shots, although many times it felt like more. I noticed if I died my last 3 to 5 shots would not register, but if I was using last stand or final stand, my last shots I fired before falling would register after I shot the opponent 3 times with my side arm. Also sniping in this game is just wrong, 90% of the trees and brush does not render after 50ft, so if someone was hiding in thick, tall grass, I would see them laying on dirt and shoot them. Also putting a silencer on a Barrett 50 cal makes the gun not kill with a headshot.
I still play Counter Strike, although it too has some bullet delay which is real annoying, especially when I see my AWP hit someone dead in between the eyes, watch blood splatter on the wall, and about a half second later they kill me and they take no damage >_>. I have a 6ms ping with one of the GunGame servers, and this delay is still there. Other then that, it's one of my favorite PC first player shooters. I really enjoy Zombie Mod for this game, but I hate it when servers have "No Reload" because then all someone has to do is sit in a hallway with an assault rifle and spam bullets to fight off the zombies. My favorite servers are part of the ibis gaming community. They have 5 or 6 CSS servers plus a Minecraft server.
I recently (I guess 400hours worth is recent) have been playing APB Reloaded. It's a third player shooter kind of like the GTA series. I like the character customization and the somewhat open world feel. Once you max out your contacts by doing missions, the game is pretty much free roaming, but there's not much to do if you're a criminal at that point. Playing as a criminal, I enjoy getting to notoriety 5 which turns everyone on the server into an enemy, which is fun when you're on a roof top with a semi-auto high precision rifle

Enforcers can get the same thing but only by killing criminals ( I think, haven't played an enforcer long enough) however, they only see criminals as enemies and the other enforcers see the player as their teammate and get penalized for shooting them. Enforcers can also "witness" criminals doing wrong and try to kill them, or arrest when using a less then lethal weapon and stun them. My few dislikes about this game are the wacky spawn system and the limited unreal engine (Unreal is not limited, but this game limits it) without SLI support. Sometimes when I kill someone they respawn 200M away from me, sometimes they spawn less then 50M behind me and they kill me before their spawn protection goes away, so I'm dead no matter what I do... The SLI problem has been around since the beta of this game. Basically some players become invisible and others glow in the dark when SLI or crossfire is enabled. This game has Nvidia PhysX but doesn't use it properly and does most of the physics calculations on the CPU, which causing massive frame drops when smoke particles are rendered. It also loads all the textures into RAM and eats through 4GB of memory for some people. The max amount of RAM it uses for me is 2.6GB, when it reaches that the game freezes for a second, and deletes a lot of stuff in memory not currently being uses. This game does require some custom configuration to get it to run right on some systems, but it shouldn't take more the 20 minutes of messing with some of the engine ini files.
I also play minecraft... IT'S ALL BLOCKS!