Does gog.com offer that, or is it only if a game is unplayable?

If you have downloaded a game and cannot get it to work on a supported OS, GOG support will try to help you in getting it to work. If they're not successful in helping you getting the game to work, you get a refund.

You can also get a refund if you have not yet downloaded the game, and you ask for a refund within 30 days of buying it.

Additionally, you can get a refund for an in-dev title, for any reason (regardless of whether or not you have downloaded it), within 14 days of purchase.

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If you have downloaded the game, it works, and it was not labelled as in-dev when you purchased it, you most likely do not get a refund.

You can always ask support, but I'm fairly certain you'll get a "nope".

Only if the game is unplayable and you have been unable to get it working with the help of support.

I didn't know this, thank for info

what is the game?

A general question, just in case...

I was just curious. :P

"Bad" is subjective.

So no.

Could be Jack Keane 2. :-P
It still has a bunch of excellent reviews from 11/14/2013 :-D

There could be some exceptions to the rule, since in certain cases a game could have serious problems.

There was such a case in the past.
The game was Dark Matter and GoG offered a refund even to users who had downloaded the game.

I wonder who ate the loss, GoG or the developer?

GoG has never been sharing business data (even though I'd really like GoG to be more transparent).

So, only assumptions could be made. I think the loss was on the GoG's side, but it should have been only money transfer plus exchange rates, since those sales should not count as completed.

There was also Armello and its "Take it up the ass"* edition. Refunds were given months after it was bought.

[EDIT] *It was actually called DRM-Free Edition. My name for it is more accurate IMO.