I don't understand people being upset with something like this, it's not like they have to buy a whole new PC to play the game like console gamers do with console exclusive games... all they've got to do is download a FREE launcher to be able to buy and play their game. It's a complete non-issue for me, lol.
Well technically there's a few things missing that Steam offers such as Cloud saves, achievements, controller support, support forums/reviews (which is something I use often).
But most of all for me is competitive pricing. When the only option is to buy from the store that hosts the game, its really hard to buy it from there because the price is fixed like a monopoly.
Compare that to Steam games where numerous stores are selling it at different prices and all are superior to Steam store's pricing. For an example I was able to buy Final Fantasy X/X-2 off of GMG for $10 compared to Steam's lowest pricing which was $15. Not only is it cheaper for me but SE gets a bigger cut from it because selling Steam keys off on third party sites gets Valve 0% which is why its cheaper to buy games on those storefronts.
I mostly buy my SE games from SE's online store and the prices there are better than Steam's.
As for me I dont mind waiting a few months or even a year to buy a game. Eventually most games will end up like Vampire Masquerade bloodlines 2 which will be (so far) available on Steam, GOG and EGS at release.