Hey Fellow Good Old Gamers,
I'm still pretty new, so I've got a question for those in the community that have been around for a bit.
Has anyone bought a GOG game and regretted the decision? Are there games on this site that are so rancid that they're not even worth 4.99? Are any of the 9.99 ones overpriced for their quality?
I've been happy with all the games I've purchased from here, but I'd love to know of any Bad Old Games mixed in with all the Good Old ones.

Megarace 3. It wasn't even worth the $3 I got it for on sale.

Most of the Ubisoft ones.

Just about all of my GOG's.. I have gotten over sixty games thru the service and I have only had the patience to play through BASS (that's one of the free ones).
The service is great, my regret is my own.

I probably shouldn't call it "bad," but I regret buying Jagged Alliance 2: Unfinished Business. Apparently I'm not hardkore enough to play Jagged Alliance without giving myself a headache.

I think quality is rarely an issue, it's more a matter of whether or not a game is for you, and/or how well it's aged (if it's particularly old).
I regret Colin Mcrae Rally 05 (I hate rally racers apparently), Earthworm Jim (pain to set up controller), Screamer (same), MDK (huge black borders you can't get rid of), Arx Fatalis (crazy load times), Painkiller (design feels cheap), Ishar, Might & Magic, Realms of Arkania, Master of Magic (none have aged well in terms of accesibility), Shogo (not my kind of shooter), and Myst (hasn't aged well).
Wow that's a long list. :P
But I seem to have learned my lesson and like all of my recent purchases.

The only buyer's remorse I have is for Vampire: The Masquerade Redemption. There is a crippling issue that prevents some GOG'ers from overwriting previous saved games, effectively giving you a 1 time save for 10 slots, which may or may not be enough for the average gamer.
That's not necessarily GOG's fault, but I do think it should be addressed, and I do regret paying for a game I do not feel comfortable with playing in its current shape.
I don't really regret Gabriel Knight 1, but it hasn't aged as well as I'd hoped.

^This.
I kind of regret buying the Earth package when it was on special (Earth 2140, 2150, 2160). I looked at them, they had the ability to design your own units, and they were cheap, but I'm not an RTS fan...
Another regret is overestimating my poor little netbook in a couple of cases, and getting games that run, mostly.
There are a few $9.99 games that I consider overpriced (e.g. Master of Orion 3, the Red Baron pack), but I'm voting with my wallet and not buying them.

Why do you say that?
Well, Might and Magic 1+2 are pretty archaic, but beyond those two.

The Realms of Arkania games.
Its so hard to actually get started on, (the character builder is unreasonably strict), I just gave up and played might and magic again...
Maybe possibly Creatures 3 as well. (I'm struggling to "get" it).
Descent 3 and Freespace 2, are pretty hard to play on a laptop, so I haven't really got into those either, (but to be honest, I did get some enjoyment in what I played of them).
Myst could be another mistake, (but I think that is due to me sucking at adventure games, and its pretty darn frustrating! XD).

Maybe I was just too young or too impatient at the time to appreciate them, but I found Myst and Riven to be obscure and confusing. Fiddle with this combination lock until you open some random door on the other side of the island... meh.
I guess there were probably hints lying around that make the game less arbitrary if you find them, but I don't like scavenger hunts, either. Thinking on it, though, I'm wondering if I ought to give the series another chance. I'm more tolerant of free-roaming adventures than I was as a kid, so I might enjoy them more.
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I regret buying Freespace.
Don't get me wrong. Freespace is pretty cool. Unfortunately, I hit a game-stopping bug a few missions into it, which I was never able to resolve. The only way I was able to progress was by downloading the remake of the FS1 campaign for Freespace 2 and starting over from the beginning.
I suppose you could argue that it's more ethical to purchase the game anyway if I'm going to play the campaign, but that doesn't make me any less annoyed that the game itself was not functional.

I assume you grew up with PC RPGs...I haven't so most are next to impossible for me.

You did not contact support?

Far Cry, Beyond Good And Evil, POP TSOT, and HOMAM3 are well worth the money if you ask me. The other games, fail.

Sacrifice and Citizen Kabuto. Kabuto is third person, i find the humor lame, and got bored of it. Sacrifice, it has the exact same error the version i warezed had. Upon launching, it crashes and freezes the entire windows. I dont even know what that game is like.

No, it wasn't that kind of bug. A scripted event was not triggering, so I could not finish a mission, despite attempting it dozens of times. I did search the internet for solutions, but all I found was "sometimes it works, sometimes it doesn't."