Most of the games I buy on GOG are games that I've either had before on a hard copy, or games that I'm pretty familiar with.
Occasionally, though, I'll come across a game that I'm not at all familiar with, and if it looks good, I'll give it a try (after it goes on sale of course).
For the most part, I'm usually pretty pleased with these unknown games, but on occasion, I'll get one that I wish I hadn't bothered with.

For me, my 2 least favorite games that I've purchased on GOG (at least so far) are:

D&D Dragonshard and Vampire the Masquerade: Redemption.

Dragonshard looks like a fantastic game, and when I first started playing it, I was really enjoying it. What I didn't realize, though (my own fault for not checking it out better), is that it's more of a Strategy game, than a hack and slash. As I started getting further into the game, I quickly became disenchanted with it due to having to create large armies to defend myself against large enemy forces. I really wanted a simple hack and Slash / RPG type of game, not an army building strategy game like this game turned out to be.

Vampire Masquerade: Redemption also started out really well. I was enjoying the game play, but for some reason after a few hours, it just got really uninteresting. I lost any and all desire to go any further. I'm not exactly sure why, or what happened, but I just came to a point where I no longer had any desire to play it, and I left it right in the middle, and have no interest in going back to it.

Of all my games purchased on GOG, these 2 are the ones that I most wish I had never purchased in the first place.

What game(s) would you say are your least favorite from your GOG collection?

Master Of Orion 3 made it into my collection, only because it was a part of a multibuy deal and it was cheaper that way...

I wish there was an option to hide gameboxes on our shelf....

Independence War (Deluxe? don't remember)

I bought it during the summer sale, and played it for 2 minutes before hating it.....

Tough question, is something I installed but didn't like less favorite than something I've had for a long while but haven't yet had the motivation to install? If so, then Gothic 2. Purely based on graphics and animation, couldn't get past them and can't really comment on story and gameplay even after piling in a whole of 5 minutes of time. So it's probably just as awesome as people say.

Messiah. Very fun at the beginning, nice TPP shooter with ability to swap bodies is all I was hoping for. Unfortunatelly, soon game turned out to be some stupid platformer with jumping over the lava and climbing high. Frustrating gameplay made me deleting this game.

It's a shame, because the main concept is great.

And yet again, I am not wondered why you get downrepped ;-P.

For me it probably is Constructor....

Hey everyone has differing tastes.....:P

I for one liked Daikatana, for example.

There's only one I've regretted, Rayman 2, and that's mostly just getting a handle on the controls. All my other purchases I spent at least an hour on research beforehand before I purchased. but I got Rayman 2 because my N64 copy is difficult to run and I don't have a memory pack for it.

For me, so far it would be Syberia (which I just happen to have finished today).

Oh, don't get me wrong: it's a great game! The scenario is really nice, the dialogues excellent, the characters worth the trip but... it's a point'n'click. And I suck HARD at point'n'clicks. So bad i barely can play them without a walkthrought. I just can't be bothered to combine items, try to find THE element of the background I missed the first xxx times I went there and so on...

So, it's the game i bought on GOG that is the least favorite to me, but by no means it means that it's a bad game! ;)

Indigo Prophecy. Shoddily done console port with controls unmanageable on PC + quicktime events (always was curious why consolers complain about those. Now I know. Guys...I'm so, so sorry for you) = completely unplayable mess.

None.
Won a few, sure, buy never bought one.

You've been here TWO YEARS and never bought a single GOG? :\

Or maybe he's bought the good stuff himself and been given appalling crap for free.

I think I maybe misread it a bit....oops. :|