The amount of games, the community features, the deals, Gabe Newell

Bad Rats

thanks for skyrim! :D

Steam can burn you more severely than boiling water!

Why not Desura? Or even Tiggit?

What makes Steam such an incredible platform?

Valve.

It was the first highly successful one?

Thanks for fortix.

It's not an incredible platform.

The games it has, the community, the features it has, the sales it has. Steam has a lot to offer really.

HAAAAAAAAAATS :D Cheap games, that i can download anytime. I don't want to clean the dust off of hundreds of game boxes... Achivements and Steam Community are great too. Thanks for the giveaway ;)

Honestly, probably the achievements / sales.

the social network

cause it's a monopoly, I don't want extra shits to play/download my game.
Also russian price (until steam locks everything)
Plus the dev community is so active and helpful

All games in one place.
No need to manually patch games.
$team $ale$
Great community :-)

Exceptionally sane and responsive support team

Volvo does

The SVN service of updates and patches, the link to developers and the all games in one library concept + the community. But it's not incredible, it's just better than the others.