That being said, I'll go over some of the basics:
Supreme Commander. If you're an RTS fan and have a decent computer, you owe it to yourself to play this game. Plus, with the patchs, it's extremely convenient because you don't need the disk to play any more. There's a very awesome looking expansion on the horizon too.
Dawn of War. Fortunately, you can get DoW with both of its expansions in one sort of mega pack nowadays, I think. Worth every penny, though Winter Assault is the weakest of the set.
Command and Conquer 3. If you liked the C&C series, buy this game. It makes a great counterbalance to SupCom, giving you a whiff of nostalgia to recharge after casually commanding hundreds of units in SupCom. It's also fantastically polished, with a huge and very interesting campaign, and also the hottest C&C girl ever. Plus the return of Kane. Because you can't kill the messiah. Balance is a bit off, but I don't feel it's as bad as some say.
A little known series, the Act of War game (AoW: Direct Action) and its expansion (AoW: High Treason) Are both fantastic 'mostly modern' RTS games. HT even introduces grievously fun naval combat to the game.
Seems like I'm suggesting lots of RTS games, eh?
Well, Stalker is pretty decent. The problem is that it's rather shallow. When you look at it, there isn't all that much unique content. Still, it's decent enough. Though there are some practically necessary mods. Mainly the handy 'repair weapons/armor' mods that let you... surprise surprise, repair your arms and armor. Fortunately, Stalker has a metric crapload of weapons. Including my favorite modern gun, the FN2000.
If you don't have it, FEAR is easily one of the three best FPS games I've ever played. (HL1 and HL2 are the other two.
) It's somewhat short, but its replay value is strangely immense, mainly because the enemy AI is freakishly intelligent and reactive to your actions in the game. It's already got one rather good expansion out, with another on the way. It's also got some fantastically entertaining weapons. Like a nailgun type thing that spears your targets to the wall ala Predator, and a particle beam that roasts them down to the bone. Other than that... Eh, I dunno. I'd have to see what you've got. HL2's a shoein, but I imagine you've already got it.
Whatever you do, though, don't get Halo 2 for the PC. It's an even worse port than the original, and that's saying a lot.
Prey was a graphically interesting game with several unique mechanics, but it felt a little too derivative of Quake IV and Doom 3 (Both good games that I recommend if you want mindless killing, though Q4 is the better of the two IMO.) It also didn't shy away from the gore. At all. Sadly, some of the weapons were rather useless, and the enemies were rather boring and dumb. Fuck if the game wasn't creepy, though.
Avoid Ghost Recon Advance Warfighter 1 and 2 at all costs. They're not only system hogs, but they are insanely unfun. Your team mates are useless in general, and the mexicans can all hit you from a kilometer away with a rusty AK from the hip while doing backflips. Even if you're in cover.
Crysis looks like it's going to be the next Half Life, so I'd keep an eye on it if you've got a decent system and a DX10 video card.
If you like 4X games, you can't really go wrong with Galciv 2 with Dark Avatar.
Anyway... what else. Oh yes, Bioshock is being released later this month. Everything I've seen about that game indicates it is going to be GOTY for 07.
Gears of War is also being released on the PC shortly. With bonus maps and single player levels. Most impressive. We'll have to see what it's like on release, though. It might end up being raped like Halo.
If you want an RPG... Go back to Baldur's Gate. None of the current RPGs have matched it yet. NWN2 sorta does in that it has memorable characters, but it's incomplete and you can tell. (There's also KOTOR 1 and 2 if you don't have them. Very good, though still not the condensed win that the BG series is. I've heard good things about Jade Empire as well, but I've never played it.)
Oblivion is decent enough, but while it has an incredible amount of content (hundreds of hours worth, easy), nearly all of that content is shallow. You can make next to no choices beyond what weapon to use, and those choices you *can* make have next to no effect upon the game. Fortunately, there is a huge number of mods, so you *might* be able to find one that makes the game a roleplaying one, rather than just another action/adventure hybrid ala Stalker with swords. Still, though, it's a very good action/adventure game if you aren't looking for much depth.
Space Sims are rather rare on the market now, so I'd just go with Freespace 2. Which is now open source, I believe. You could also get the Privateer remake available, which is also free and very snazzy. If you can deal with the horrible voice acting from the original game.
I've heard good things about Beyond the Red Line, a nBSG total conversion for FS2, but I've not had the chance to play it.
There've been no good pure adventure games in recent years.
I don't do racing games, so I won't recommend any.
Moving on... For H-Games, I recommend Moonlight Climax. If only because it's simple. There's no real story, just a whole bunch of hideous creatures/tentacles filling a girl with gallons and gallons of semen.
Meh, I can't think of anything else.
