It seems possible now that Halo:CE, Halo 2 and Halo 3 have been listed in the Steam apps database. Halo Series Coming to Steam? Search · Steam Apps Database Thoughts?
Too little too late perhaps? I'm pretty sure if someone liked the PC version of Halo Combat Evolved they would've got an Xbox and Halo 2 (considering the amount of time that took to come out on PC). I can't see it being that successful (another example would be Gears 1 for PC....). Besides Halo fans curious to see what it'd be like on PC who would buy it?
Seem's strange timing though with Microsoft/Bungie turning off the Halo 2 Multiplayer just recently. I was hoping Halo 3 to be released for Windows 8 Metro though as they used Halo 2 to launch Windows Vista and Windows 8 needs something ground breaking to get it going.
I'd like to get the whole trilogy on PC all in one piece. So no activation hell for Halo 2, different key for Halo 1, etc. Just all 3 games working with one installation. I'm not too fond of Halo 4 myself, a single game 'doomed' to be a trilogy takes away potential on the campaign even though the multiplayer is alright. I likely won't get Halo 4 until they completed the game (read: trilogy) and release it in one piece (read: package).
These Halo games are old and if possible Microsoft would like to make more profit off of them, like anyone would with their products in the market. Halo 3's fun online last time I played (months ago) but CoD MW2 got me.
5+ years after release is a little late, would be nice to see Halo 3 in a much higher resolution running at 60+ FPS however. Sadly the games are only ever going to be a success on PC if released at the same time as the console version, yet the games are ported years later and Microsoft wonders why sales are low. Regardless i would likely pick it up in a Steam sale at some point.