...it doesn't "feel" like a Fallout game. EDIT: My use of the term "hate" below should be read as somewhat light hearted.
I HATE the dialogue menu. I hate my player having a designated voice and backstory. I hate being assigned a wife/husband and child. You remove my immersion by doing that.
I hate the perk system. I want my skill % back.
I hate VATS not stopping time.
I hate the vast, endless and primarily useless amount of pipe guns in the game.
I hate the power armor GUI. I hate using power armor, period. I hate the clunky interface used to customize it on that rack, having to get in and out of it.
I hate the amount of "stuff" I have to juggle in my inventory. I hate how ridiculously heavy some things are versus others not weighing anything at all. Cut the weight of weapons and armor, please.
I hate the UI for customizing your town. I hate being forced to level my charisma and choose a perk SOLELY to establish supply lines (what, these people can't do that crap on their own?? come on. Why do I need a PERK for these people to think, "hey let's trade stuff between us" They can't think that up on their own?).
I hate how fast some enemies move, forcing you to use VATS, which I hate using anyway. (Stingwings, anybody??)
I hate how slowly ALL melee weapons swing, especially fists and one handed weapons.
I hate not being able to dual wield (What is this 1992? come on guys).
I hate that MODing is going to have to be done to make this game into a 'real' fallout game for me.
...but I do love having a Mr Gutsy companion, or a big BoS Sergeant companion. I do love the graphics. I do love the questing and story. I do love the voice acting.