You do NOT need to finish Half-Life 1 to play Half-Life 2. So if you haven't played that game, go pick up the Orange Box. It also contains Portal, the best game so far this generation.

I'm currently playing Racedriver: Grid and The Chronicles of Riddic: Assault on Dark Athena. Both are well above the expectations I had on them, but Grid in particular is an amazing experience.

If you like Diablo, I strongly suggest you take a look at Torchlight. It's a Diablo clone with a very good interface, which makes it a pleasure to play.

if you are into rpg's you may want to check out some older games like jade empire and knights of the old republic 1 & 2.
A newer rpg that is a must play is the witcher, so check that one out too.

I haven't played Tropico 3 yet so I don't know. But in my opinion Tropico 1 was better than Tropico 2.

Yeah, I think STEAM deals are generally the same around the world, they are quite old games, so they will certainly be cheap whereever you are.

Anno 1503 is probaly the worst game in the series. Still good though.

Get Anno 1404. It's awesome.

Tropico 3 is practically Tropico 1 with prettier graphics. If you have first, don´t bother with third.

You can try Deus Ex, IMO great geame too. From strategy, Try Heroes of Might and Magic, IMO HOMAM 3 is the best. Or King´s Bounty, same princips as HOMAM

1 - get yourself on Steam

2 - get yourself Orange Box

3 - maybe get Half Life Source if you really want the backstory

4 - get yourself STALKER - patch it, then get the mods that improve graphics, performance, etc. and enjoy perhaps the best FPS/RPG hybrid around

5 - get yourself Grim Fandango and Deus Ex and System Shock 2 (if you don't mind the dated graphics they are amazing)

6 - peruse Steam for games/deals that appeal

I've been playing L4D2 and Champions Online like it's my 4th job (I have 3 jobs) and they're both great games.

Warcraft 3 + Frozen Throne + Dota Map = The most time I've spent on any game ever. I must have played some 10000+ matches on Dota over years.

Actually, the more I think about it, it's probably way more than 10000. Mmmm Dota.

Edit: On Champions Online, MMORPG with cool customization. There are no classes, you can choose powers from some 20 powersets and mix and match all you want, and the costume creation is a blast. Great part too, most MMOs suffer from a high amount of downtime (read as walking/travelling time). This isn't the case in CO, you can get from one side of the map to the other in a few minutes once you get a good travel power.

I remember playing WoW and it would take a few hours of play to get anywhere. I can log onto CO, play for 20 minutes, and finish like 5 quests, it's awesome.

I see you have Warcraft, you may want to try Age of Kings (with The Conquerors expansion), it's a great RTS and there's still an active community for it if you really get into the game. Single player can be nice but multiplayer is definitely where it's at for this game, so if you're not planning to go multiplayer it's not as worth.

Have you tried "plants vs zombies"?
IMO it's quite good