It's pretty rare for me to jump in and buy a game without knowing a lot about it beforehand. So that tends to keep the "sorry" games out of my collection. Though of course I've played my fair share of them.
I really enjoy gaming and I think that even sub-par games almost always have a redeaming feature or two. That's why I'll usually suffer through a game that I might not be enjoying all that much. Though even I have my limits.
A few recent games that I just couldn't finish:
Haze - I know this game get almost universal flak but it's well deserved. Just another bellow average shooter so I didn't bother wasting my time.
Lair - I played this prior to the patch that allowed the use of the joystick on the SIXAXIS/DS3. The controls ruined the game and I quit playing.
Full-Auto - I thought it would be like the next Twisted Metal. It's not even close. I played it for about 1hr and then sent it back to GameFly.
Front Mission 4 (PS2) - This is a tough pill to swallow because I really enjoyed FM3 on the PS1. Sadly SE stripped anything fun out of FM4 and what was left was a terribly vanilla SRPG. I tried on 3 seperate occassions to get into the game and I couldn't.
Thankfully, I do a lot of research before I buy a game. Therefore, I don't have to worry too often about putting up with a poor one. Of course, there are always those titles that seem to dazzle no matter how they're looked at and are bought only to reveal that they're not as awesome as they had previously looked.
So, how easily do I give up on these sorry games? From what I've found, not easily. After all, it's hard for me to spend months looking at a game, twiddling my thumbs in anticipation, only to to get it and stop playing within a few hours of popping in the disc. I always try to revisit, hopeful that I'll eventually get sucked into the experience. It's not really fair to play a game for, say, only an hour because it's such a small portion of the experience. For example, my friend once told me that he couldn't get into FFX and I asked him how long he had played it. If I remember correctly, he said about an hour. I laughed.
I always try to look at the positive side of things when I find myself becoming increasingly frustrated with these titles. As I'm playing, I'll look at what the developer does wrong and think of how they could improve upon it or completely get rid of it. I'll also look at what the developer does right and which direction they might go for a sequel. In any case, it's sometimes just fun to play a dud and laugh with it, or rather, at it.
I'm actually pretty proud of how often I put up with games that don't excite me. I didn't enjoy Oblivion but I put probably a dozen hours into the game. I pretty much loathed Far Cry 2 but I buckled down and finished the campaign. Assassin's Creed was a huge disappointment, probably one of the biggest I've ever played, but I also finished the game. Fallout 3 was another dud for me but I revisited it and beat it after a good year-long break. The only game that I haven't given a fair chance to is Unreal Tournament III, another game that I couldn't wait to have. Of course, these long summer months are pretty empty. I might just have to revisit the shooter.
I bought Brink after watching several trailers. I traded it in less than three hours after purchase. That is the one and only time I've ever EVER had a bad experience with a game up to a point where it made me angry that I'd bought it. Me and my friend both bought the game at the same time, as we regularly do so we can play together online.
The problems started as soon as I started it up. We couldn't even get in a game together. It was shocking. The graphics were absolutely diabolical as well. I'd never experienced anything so bad in my life. If there was an award for 'Most Misleading Trailer in Gaming History' then it would definitely go to Brink.
I honesly don't think there is one positive which I can think of for that game.
To answer your question. If I play a game after purchase, for a couple of hours and it doesn't feel right or I don't like it. I'll usually take it back or it'll collect dust on my shelf and eventually get traded in.