Darksiders II. I was so excited - you play as Death, you go around hacking up massive demons like the first game (which was awesome), but now there's Diablo-style RPG elements! I love that kind of game!
Unfortunately, they fucked up the story and worldbuilding by bringing it in the most bizarre directions possible, the RPG elements were very disappointing and had zero depth, the puzzle elements from the first game were much reduced, combat was a dull mashfest, and overall it was much too easy, with my beating sidequests while 10 or more levels underleveled much of the time on the hardest difficulty. It was by no means awful, but there just wasn't much to it, unlike the awesome first game which holds up much better.
I'll also say Arkham City, though to a much lesser extent. The story and main quests were all great, and a lot of the collectibles were interesting and fun, but the sidequests were so bad. Most of them abruptly ended with nothing resolved right when they seemed like they were about to get somewhere really interesting - either blatant sequel bait or Rocksteady ran out of time, I'm not sure which.
For books, the Riftwar Saga. It's the first trilogy in a huge series with some 30-odd books in it, and I hear the second trilogy and the Empire spinoff are the best parts, but this first trilogy was kinda meh. The first book was awesome but each after it got steadily lamer, with the third one almost running on absurd deus ex machina, where bizarre magics that were never mentioned before suddenly threw the heroes into trouble and then even more bizarre things got them out again - often in extremely ridiculous fashion. The author also had a habit of presenting a moral quandary to the characters by putting their goals at odds with each other or with the realm, and then abruptly resolving it without anyone having to grow or make a difficult choice by picking a character and killing them off so that they're no longer an obstacle. "Do I potentially betray my uncle? I know he'll drive the kingdom into ruin if I let him continue, but I'd throw the nation into a war of succession... oh wait he got stabbed to death. Problem solved!"
