I've been thinking about this a lot recently as I've started to become really disenchanted with games in general.
Mostly RPG games. Western ones in particular, Baldur's Gate, Fable, Oblivion; they just seem to all have the same world and really boring combat systems. I mostly play them for ages, grinding away without realising there's no fun. I just can't understand why no-one seems to have made a really detailed RPG with a decent combat system. JRPG's used to be my poison, I had something like 140 hours on FFX and 60+ on 7, so obviously I enjoyed something about them (story, world and character development), but the combat system is, in retrospect, zzz. So I guess the answer is: Western RPGs for being entirely generic in story and world, and nearly all RPGs for tricking me into believing the actual combat gameplay was fun. The only one I can really think of that I've played that does this is the Kingdom Hearts series, even though the story made soul cry and the characters made my fingers itch.
(On another note, why do nearly all fighting games play like your characters are glued to the floor? OK SSBB I guess. But all the other big ones (Tekken, SC, Street Fighter, etc) make me feel so limited and immobile. The most fun fighting games I've played are the damn Touhou ones. That shouldn't be true.)
It's not like I even want to attack these Genres though. The RPG genre in particular is the game type I would most like to enjoy, and I can see what a good RPG would be like in my head. I just can't believe that it doesn't seem to exist. I guess action adventures with a few rpg elements are the closest I'm ever gonna get. Please do point out any glaring omissions I've missed, so that I can play them.