gyokzoli: AFAIK you can still play SS2 without Steam if you want.
I'd really appreciate a definitive answer, should anybody here decide to drop the 4,000 coins on it. I already have pending payments for Wasteland 2 and Banner Saga, I'd love to be able go for higher tiers on both, and I'm trying to save up some cash for the month, so if I have to activate Serious Sam 2 on Steam (and worse, if I have to launch it through the client), I may as well either wait for the inevitable 75% off or better on Steam or wait for it to show up on GOG.