Sorry Raze, as you can imagine i cannot agree.
I would suggest to make a different bargain:
i pay the full game and and if, after playing 3 days, everithing is ok for me i confirm payment, otherwise i automatically get refund and the steamkey become invalid.
But i don't think that the software house could agree: why i should agree to buy a product that could not work and i have to pay with "working money" ?
Saying that " it is impossible to release a completely bug free game" is an excuse because
1) the bug we speak about make the game unplayable
2) your sentence is like "if everyone is a thief, why i can't be a thief too?"
Would you buy a stair without all the steps, knowing that when the left steps will be ready they will be send to you?
When i bought the game i knew that i could find bugs, but i thought i would be able to play.
Why i can't get refund and get/buy again the game when it will be fixed?
Lastly, this is a digital versio of the game: it means that there is no box, no manual, no written story, no map no everithing, the only thing you get is the software, and it is not working.
I know that programming a game is something hard and difficult, and i also know that there are a lot of different computer versions, but you, as company, also know that you are selling a not fully working product, so you should create a different seller policy, it is not right to sell something that can't be used.