Lag. Anyone who plays online games should have this for their top answer.
"Artificial" Difficulty - I'm not talking Dark Souls. I thought that and Demon's Souls was punishing but fair. I'm talking something along the lines of enemy AI being damned near psychic. Perfect Sims and Dark Sims on Perfect Dark, Veteran Difficulty on CoD are some examples.
Infinite combos should not exist. I was playing Anarchy Reigns online, and mixed with the lag I had, I could never break a combo, and consistently getting knocked into a long combo by someone who on my side was clear across the map. Lag and timing issues made combo-breaking impossible, if it was in the first place.
Let me level in piece you bastards. I played WoW for about a week on a private server that had open PvP. It was even modded so that only Shattrath(sp?) City was safe. Needless to say there were "Donors" who had 3000 or so of EVERY STAT (Donating gave you free T6 gear, and special gear that gave 200 to every stat for EVERY SLOT, except trinkets) And of course people camped the starting areas. Freaking lvl 70s.
I played longer on the real servers and played the last expansion (Cata, not Panda-land) on a PvP server. I ended up getting camped an entire guild when I was level 50 or so. Most of them were level 85.
UNSKIPPABLE CUTSCENES: I can see forcing the player to watch it once, or if it's masking a loading screen (Show me a progress bar if I try to skip one of these, please)
Verbose Tutorials: I've been a gamer for over 20 years, I know some people are starting their first game while this is just another in my collection, but you don't need to treat me and every other gamer like they are pants-on-head retarded. I don't need a dialog box telling me how to move or "Press X to when the "Press X to use" icon shows up, which is ALWAYS shown as, who'da thunk it, an X, and usually a caricature of the PC doing an action, or even words.
Other (Online) Gamers: I like multiplayer games with friends. WITH FRIENDS. I abhor the average online gamer though. whether it's the elitist "pro gamer" who apparently sleeps with everyone's mother, the trolls, or the people who want to get good at a game without any effort (I saw this a LOT in WoW. The game is not hard to be decent at. I figured it out and was usually the top DPS in any run I went on. I had one person who CONSTANTLY bugged me about how to lay because we played the same class. I linked him to a site I used, and he complained that he didn't want to read anything, he wanted me to teach him... this was through the in game chat too.