World of Warcraft - It was very easy to for me to see why this game was/is so damned popular. I never played it until I got into college thanks to me gf who told me to play it with her and a friend. But, I got bored to tears and only continued playing because my gf played it and a few other folks I knew. I thought the art style was really slick and I liked the class I played (ranger, and I always tried catching pets no one else seemed to have), but outside of those things. Meh... I got bored pretty fast and once I got to one of those territories where you could attack the players from the other faction, I did. Then I got bored of that and essentially quit playing. This sort of goes for most MMOs. I usually try exploring the game world, interacting with the various NPCs and doing all the quests to see the world get fleshed out but I hate the aggro and it made exploring the world rather tedious.
Sins of a Solar Empire - It was a fun game but every time I started a new game it ended up feeling completely the same no matter the size of the system or galaxy I played on. I saw the addons that were later released but none of them made me want to go back and play it. I did enjoy it I'm never going back to play it again. I think the biggest thing was that carriers made no sense and I had to do a lot of micro-managing. I know the add-ons alleviated certian issues but I just...cannot for the life of me garner any interest back in the series.
Sports Games - I played a lot of Sega Sports Y2K - Football, Baseball, and especially the Fifa games. (Never really did the racing games, *yawn*.) But I could only play them in 30 minute increments before I got tired and bored. Don't get me wrong. I enjoyed the managerial aspects of the games (especially Fifa because of the tiered leagues) but even with those I got bored as well. I don't think I own a single sports game right now...
Grand Theft Auto III- And maybe the entire series. I thought the game world was great and fun to play in and did a lot of other side quests or whatever they were called. Never did the main storyline (never do in these types of games) and just did everything else as it didn't really interest me. I just mucked about mostly and rather enjoyed it more watching my friends play but when it came to me. I ended up always switching to something else. Nowadays I can't even touch a GTA game. However, the radio talk show guy was too much fun listening too and I still quote it to this day.