DUke Nukem Forever. yes, I DID IT

Psychonauts, when it was on sale for $2. I now have 141 games on my account. :/

I got HL2 as a gift, so i'm not sure if that counts. Apart from that i'm guessing Mass Effect.

Yeah like most in this thread the first game I ever purchased that required Steam on my PC was Half-Life 2. I would probably guess that the first game I ever bought in the Steam store was World of Goo, which to this day I have never beaten despite enjoying many of the levels I played through.

Left 4 Dead was my first

Amnesia: The Dark Descent was my last

Mine was Psychonauts if you don't include the Orange Box that started it all. Actually, I had HL2 way before the Orange Box, but didn't realize you could gift extra copies so I gave my old steam account to a friend and started a new one with the Orange Box. Owell, I think after more than 140 games its a bit too late to trade accounts back :P

First game I ever bought using the Steam store was Braid. Otherwise, Half-Life 2.

Magicka, because I bought boxed copies of all the HL stuff and around the time I got Magicka was when I went fully digital. Haven't bought a boxed game since.

team fortress 2 for 10 bucks. two weeks before it became free to play

Dragon Age Origins: Ultimate Edition was my first purchase I believe.

Space Empire IV. Don't judge. Rome: Total War was my second. I bought Half-Life 2 a long time afterwards.

First game registered: Rag Doll Kung Fu

First game bought via Steam: Zeno Clash

I had my free Steam Account for quite a while to play the free games (Alien Swarm, Half-Life 2: Deathmatch), but I finally gave in when Super Meat Boy was $5 on the 2010 Christmas Sale. And then I added The Orange Box, and some indie packs, and the games kept piling onto my cart...

Edit: Oops, SMB was $3.75, not $5.

E.Y.E. Divine Cybermancy

My first game was Left 4 Dead 2

Warhammer 40,000: Dawn of War II Retail (Inter) ... heh, weird ... would have thought it was some valve game.

The original Portal... If I'm remembering right...

First registered: Orange Box
First purchased: UT3

I got Steam together with Half-Life 2 and the internet.

Half Life 2 with the creation of my steam account back in 04-05'. After that I think I entered my product key for Half Life 1 which gave me the Team Fortress mod, Blue Shift, Counter Strike mod, and I think Day of Defeat. Remember my mind was flabber gasted by all the cool mods that were with HL 1 as I really didn't follow the mod scene back in the day. In terms of purchases gotta remember steam was pretty iffy back in those days and digital purchases wasn't seen as really viable. I think my first actual purchase might of been Half Life episode 1.

Hitman: Blood Money, according to my purchase history.

Before that I also redeemed Portal and bought the Valve complete pack but they don't really count.

Not counting the complimentary Half-Life platinum pack, AvP Classic 2000 was the first one, followed by Deus Ex: GoTY Edition. Both of those games I had already played and loved, due to teenage pirating, but I guess I felt that they deserved a proper purchase once I started making some moneyzz.

Kerbal Space Program.

I redeemed Portal and TF2 but the first game I bought from the Steam interface was KotOR.

This was in 09 since after the death of the CRPG I moved to consoles.

Counter strike was first registered and like everyone at the time I wasn't happy about it.

Max Payne was first purchased apparently

First game activated: Half-life Platinum Pack (I'm pretty sure the actual name was Half-life Generation 3, not sure why the name is different in the Steam account history).

First game(s) purchased: X-COM Complete Pack (i.e., the original X-COM games - UFO: Enemy Unknown, X-COM: Terror From the Deep, X-COM Apocalypse, X-COM Interceptor and the abysmal X-COM Enforcer)

Audiosurf. Jeff kept bringing it up (with good reason) in the site's early days, so I had to see what it and this "Steam" thing were all about.

Day of Defeat: Source and Garry's Mod

The first game I had on Steam was when I redeemed Empire: Total War. The first game I actually bought was Half-Life 2: Deathmatch

Like most people, probably, i'd already purchased physical copies of both HL2 and DOD:S. The first game i actually bought in the steam store was Left 4 Dead.

Registered: Half-Life

Purchased: Fez.

Commander Keen complete pack

The Walking dead or the Wolf among Us. But ONLY because It's a point and click game.

Yep, the reason Steam was originally installed on a computer I owned.

activated steam with HL2 in 05, but my first purchase was actually HL2 Episode 2

Audiosurf.

A retail copy of Left 4 Dead is the first thing that I registered on Steam. The first thing that I bought through the Steam client was the Far Cry Complete pack, which (at the time) included Far Cry 1, 2, and any DLC.

Same, except it was more like 'forced to play on Steam' instead of 'the first game I bought on Steam' I think The Orange Box may have been first game I bought on Steam. (£25 for HL2, HL2:E1, HL2:E2, Portal, TFT2 & Peggle EX: Orange Box Edition! how times have changed...)

I just checked my account, Morrowind Game of the Year edition.

Registered: Fear 2: Project Origin

Bought: Osmos ---- I know this one is kind of strange. I actually remember my friend playing this and it looked interesting, so I ended up getting on a steam sale for $2. Right after that (literally 3 days later), I bought the phenomenal ARPG known as Torchlight.

Original Half-Life because Valve was moving the CS servers from WON to Steam. Still have my 2003 account.

Civilization IV when I realized my Mac could run it. I also bought Civ V, but my Mac (2008) can't run it very well. That's all, because I own a Mac.

The source premier pack, which don't exist anymore. A bundle that included Half-Life 2, HL2 EP1, HL2 Deathmatch, Counter-Strike Source, Day of Defeat Source and Half-Life Source.

Half-Life 2 - Episode One

The Orange Box

Prey.

Half-Life 2. Though the launch was so plagued with issues it wasn't funny. I was one of the lucky ones who was able to play it at launch with little issue so I didn't see a problem. I also didn't think it would be half as successful as it ended up to be. I'm glad they became the example to the industry and in my opinion they saved PC gaming by creating the environment that we all enjoy now.

Ten years ago Steam was a nightmare you had to endure to play Half Life 2. It was basically the sign of the death of PC gaming.