I have 2 off the top of my head:
Agarest: Generations of War - It's a tactical turn-based JRPG! It's a story that spans multiple generations! It's got dating sim elements that actually influence the story! It's got a medieval fantasy world full of monsters! It's got a (semi) mature plot full of political intrigue! It's got waifus! I mean geez, this game couldn't have been better marketed to someone like me. I couldn't wait to try it, and when it finally got ported to PC, I jumped on it, day one, including all it's unneccesary DLC! The problem is... the combat... oh the combat... is SO UTTERLY BORING and confusing in the worst kind of way. You don't have interesting backgrounds to look at, you don't have fun skills to use, you don't have height maps, what you do have is the most backwards asinine combo system where battle placement has little to do with tactical maneuvering and more to do with positioning your guys in the right spot to trigger a multiple combo. The fights are long, uninteresting, and dull, and to make matters worse the map gives you hundreds of these boring super long fights that aren't even plot related in-between the actual story. Geez Agarest, you had the formula right but you wasted it on such subpar gameplay!
Divinity: Dragon Commander - Okay... wait wait wait, we have a chance for redemption here. It's another game all about strategy, political intrigue, and waifus... we got this! Dragon Commander looked awesome, combining the political strategy of Democracy with the turn based campaign map of Total War, and the RTS aspects of Command and Conquer... with a dash of sexy fantasy girls, interesting NPCs to talk to, and a fun fantasy world to explore, coupled with some interesting gimmicks (like controlling a dragon on the battle map). It looked awesome! It wasn't... it's not terrible, it's not bad, it's not full of glaring bugs or bad design choices per se, it just isn't by any measure good or memorable. Every gameplay aspect of the game feels stripped and bare, even with upgrade trees and multiple units it never rises to the point of feeling interesting or dynamic. It does so many different things at once but never once does a single thing great. There's nothing to stand out really except that this one of the only games to mix all these things into one, it's such a shame it didn't do it that good.