Damn this is hard..... so 2002 is is far back as I can go... grr...  Love how so many people picked before 2002 so I will pick a few games in each category to also break the rules...

Shooters- Half Life 2, Battlefield 2 and Team Fortress 2. (runner up Arma 2 I wish I had more time for this game its hard but so damn rewarding!)

RPG's- Dragon Age Origins, Kotor (Kotor 2 would of been better if Lucasarts didn't rush Obsidian with only a year of development time) and Skyrim (just waiting for developer tools to come out and more mods) (Runner up Mass Effect series (if it had so more game mechanics of Kotor like melee and hand to hand I would of exploded but its still a great series none the less)

Strategy- Homeworld 2 (love the mods this game has and yes HW1 is way better), Sins, and Sword of the Stars (Hope Sots2 is fully up and running in 2-3 months) Man I love sci fi. Runner up Distant Worlds- its started out rough but this game keeps its rate of improvement omg it could top my list for favorite sci fi game.

Turn Based- GalCiv2, Civ IV, Medieval Total War (I want Civ V to be here but no, choices the company makes and the skeleton crew to work on Civ 5... gr... One can only hope for a amazing expansion.)

MMO- Eve Online, (TOR has some stronger areas like its better in single player department and group missions than eve but thats it)

Fighting Games- Super Smash Bros Smash and Brawl (this game is pretty damn close to perfect in my book and also Link and Sheik for the win!), Dead of Alive 4 (I don't play many fighting games so sue me)

Racing- Forza 4, Burnout Revenge, F Zero GX (why the hell hasn't Nintendo pushed out another game is beyond me, love the music and how crazy hard this game can get and oh yes Captain Falcon!)

A lot of classics came between 98 and 2000. X-Wing Alliance, Jagged Alliance 2, Unreal Tournament. Anno 1602 came out in 1998 too... As did Heroes III. Seems like all the staples of many series came before the last decade. Hell, even Diablo 2 came in 2000.

I really have no idea which game would be the best of this decade. Most of my favourites came earlier.

I'd have to say the best game I've played in the last 10 years would have to be the night I got my woman

edit: but aren't games supposed to end at some point?

Not the great ones...22 years and counting here! 

But back to computer games, Elite. oh wait, 2002 the limit.  I really enjoyed Mass Effect, Sins and GCII.  I'd have to throw darts to rank those.

I won't disagree with any of that, except the construction tool crossed with an ant farm bit. That sort of fails to give credit for all the interactions going on in that "ant farm", some of which are so deep it allows players to literally craft their own unique narrative every time they play. No game gives you the amount of details or interactions necessary to ever pull that off. Maybe Skyrim comes close if you consider visual details good enough.

And honestly I think Dwarf Mode has qualified as a game for a long time now. If {x} Tycoon games are games by virtue of what happens in them, Dwarf Mode is too.

So yeah, while it's inelegant, inefficient, all that jazz.....it's that way by virtue of how much work has gone into it. As a simulation it has no equal except MAYBE Aurora, which is even less graphical/intuitive. Like I said, just based on the scope of the game it really has nothing to compare itself to. What other game has stayed in constant development for over a decade at the scale and level of detail as DF? In this day and age when people get hyped, devour a "GOTY" title in two weeks and defecate its memory, never to look back again, I think that's worth a lot.

Cheap shot. My best games have unfortunately ended. Hopefully a classic is coming this decade.

No one can just pick one? 

Surely there has to be a favorite for every gamer. I think Tiberian Sun was more than 10 years so I will now say GCII:TA:seanw3's ultimate sci-fi mod. 

Civilization IV, Fall from Heaven Mod

Maybe I just have no taste, but I tried Sword of the Stars and was so bored and turned off by the game in the first 20 minutes I never played it again. The same with Dragon Age:Origins. I played for about an hour and a half and just was not into it at all. I felt like I was playing WoW with more people to control. So dull.

Mount and Blade:Warband was amazing, but it never finished and they never improved the siege so it is one of the best games of the past 10 years, but only because for me there weren't that many good ones.

Well Sid Meier's Alpha Centauri, the original Shogun: Total War, and N64's Goldeneye are too old, apparently, to qualify as "last ten years"...what a shame...

Barring those precious jewels of my childhood, I'd have to say Sins is legitimately my favorite now....

Not sure if this was directed at me, but Medieval Total War did in fact come out in 2002.    

No, it was directed at everyone including 2001 games.

Morrowind

Civilization IV Fall from Heaven Mod and RTS Lord of the Rings

Planetside

Three factions, fluid, epic base sieges.  Nothing like it before or since.  Expansion pack ruined it IMHO.  More real estate coupled with a fragmented and declining player base made it feel barren.

A bit hard to choose....

But ultimately, I have to choose:

First time I tried WarCraft II, I liked it. When StarCraft arrived, Blizzard became THE Gamedeveloper for me.

When I tried Dawn of War in 2004, it was a new type of RTS and I couldn't go back to StarCraft. Just too arcadey. Didn't like it anymore.

A friend made me try Company of Heroes: Tales of Valor in 2010 and I liked it. The more I played, the more I liked it. After a while I was determined. Relic with Dawn of War and Company of Heroes are the new RTS makers for me.

Dawn of War: Dark Crusade is a fantastic RTS and Dawn of War II I've just started but Company of Heroes is just solid.

I'm still looking for people to destroy in 1v1 btw....

Civ IV BtS:  Brilliant game on its own.  Quality mods, and mod mods, are a bonus.

JA2 Gold came out in 2002.

Bloodlines might have been the only time I've been scared in a haunted house.

Am I the only person in the world who enjoys Civ V more than Civ IV?

Since we are in the last ten years Total Annihilation and Master of Orion II is out.

Last ten years:

1. CIV IV

2. Kings Bounty

3. Skyrim

Honorable mention to Defense Grid Gold, but its more of a casual game.

PC: Team Fortress 2/ Civ IV in a tie.

Console: Virtua Fighter 5

Morrowind

Past ten years? But most of the best games are older than that .  Even if they had crap for graphics.  Heh very nice ones being listed though.

I'd have to say Civ IV. The amount of hours I've put into that game far exceed any other. I have mixed feelings about everyone who quantified their Civ IV choice with the Fall From Heaven mod. I love the mod and got a lot of enjoyment out of it, but it wouldn't exist without the strength of Civ IV as a game itself.

As for Civ V...It's the first Civ game I couldn't get into since I played the first one on my 386. It looks pretty though. 

Dawn of War II

From a pure value staid point I`ve gotten more enjoyment for the money from this serieis then anything I`ve ever bought.  I paid $30 each for DoW2, Chaos Rising and Retribution.  I`ve logged well over 1000 hrs on these.  It has been absolutely fantastic.  It has the best music and sound effects, Voice work I can remember.  Those are important things for me.

The MP is really where it takes off.  I`ve never played an RTS MP before.  I became obsessed with this MP.  Incredible!

I would highly recommend it.  I`ve never played a game as much as I`ve played this series in last 15 years.

Eve Singleplayer ie Freelancer