I'll only list out stuff that's about the actual games, nothing about the media (e.g. bitching about "casuals," bullshit reviews, etc).
DLC.
Reasons are all over the thread, but basically, we're being charged extra in order to play the "full game." Screw that!
Download-only games.
I don't actually hate the downloadable games in question - no, not even close. I just bought Castle Crashers recently, and honestly, it's one of the best games of this gen (seriously, it's that good). The problem is I can't take the damn game with me, it's linked to the console (or gamertag). I want these games in a physical format, somehow!
Consoles imitating PC's (inheriting its problems).
naznatips said it best - required installs or patches, mixed with slowdowns hurts. Add to that the focus over online at the cost of local multiplayer, and games designed entirely around the assumption I have an HDTV (often unreadable text).
Multiplat games have a split online userbase.
A few friends with PS3's and Modern Warfare 2, the rest with 360's Modern Warfare 2. I'm forced to go with the 360, so I can't play the same game with the PS3 guys. I really hate this shit.
Higher pricetag on games.
I won't be falling for this one. Lower the price on games, or I'll wait until they drop in price, or even buy and sell them used. $60 for most HD titles, or $50 for a short single player game isn't going to fly - I don't care how much it cost the devs make the game, all that matters to me is the value (fun / entertainment) I get out of it. On that note, I don't want a PS3 for its Blu-ray player, I simply want the console for its games - don't expect me to pay $500 for a videogame console.
Removal of desirable features in the name of revenue.
This problem is not unlike the DLC issue. Take the PC version of MW2 - they removed dedicated servers, which is not only terrible for latency reasons, but makes little sense unless they want to charge us for more bullshit DLC (like maps that'd normally be free). Blizzard is going to remove LAN from Starcraft 2 (to fight "piracy"?), quite a difference from the Blizzard of old that let us install multiple Spawn copies (multiplayer-only) with a single disc.
I think most of the awful things this gen has brought us is linked to the rising development costs. Instead of trying to bring in more customers (like Nintendo has been doing), the videogame companies are trying to milk the current costumers, us, for all we're worth. I'm boycotting some of the games in question out of principle, these practices are unacceptable.