Breath of Fire 5 - The most nonsensical BS game mechanics I have ever seen in an JRPG, and the whole JRPG genre is pretty much what happens when good gameplay and novel ideas go on vacation in the first place. Though kudos for trying something new I suppose, but it doesn't change the fact that it sucks ass.
Advance Wars Days of Ruin - It's not bad per se, but compared to the rest of the series it's a huge disappointment. It's like 25% as much content as the games that came before and there is not much left after that aside from an easy mode campaign. Coincidence that the series seems to be dead since?
I'll throw in an entire console, the Nintendo DS. Compared to how much it sold and how much it was hyped and how many games were released for it, the overall quality of the games was lackluster. There were some great games of course but I could list half the system's library as disappointments. It should have been the turning point were handheld games were finally up to par with console games, but at the end of the day most released are barely passable and that only because they were for a handheld. Also the dual screen feature is pretty useless. At first we had some gimmicky experiments like holding the DS like a book or even a clever puzzle involving it here and there, but then devs quickly realized how useless it actually was and they all went back to showing minimaps and inventories on the second screen. How amazing...
Duke Nukem Forever - They should've just canceled it and did a different Duke game entirely.
Yes, this was so bad they would have been better off not releasing it. I mean from a game standpoint, I'm sure it made financial sense since the name alone had enough attraction power to move some units.