Probably COD at the moment. Its currently dominating the gaming world. MoH has been slated quite a bit but I've not played it so can't comment.
And Crysis is crysis. What more needs saying?
CS:S is awesome too but very outdated and its increasingly difficult to find a "normal" unmodded game on there now lol That said I still love playing it XD
I easily found normal not moded servers, obviously the sound and stuff like that has been changed on most of the server I play on, but that only makes it better. But I do agree some of the mods are terrible e.g. zombie mod and stupid stuff like surf and bs like that.
I'm more into game play rather then graphics which is why I don't play CS:S as it's crap.
the UK CS scene is completely dead, yes there are still a few teams and leagues, public is dead as it can be, an cheats are too easy to come by as everyone does unless you're playing on AC which is just offical games really..
I bought BlackOPS it's just finishing downloading now
Black ops is a good game, I still prefer Cs:s but that is probably most like becuase of the poeple I play with, the funniest guys ever, and the atmosphere on those few servers is just great, however bear in mind that they are not uk server so I do indeed understand what you mean by saying that uk css is dead.
Zombie mod on counter strike source is a required taste but if you love zombies it's fraggin' awesome!!! Team fortress 2, killing floor are really popular. But black ops has the crown
Battle Field Bad company 2 is IMO the best online FPS since modern warefar 2. Black ops is good. But BFBC2 is what i keep coming back to and it got new maps not long ago try it. It is defenitly more fun imo than black ops, and you get to fly helicopters, tanks. More team based as well. My favourite online fps for 2010