Wikipedia's article should get you up to speed on the plot:

http://en.wikipedia.org/wiki/Half_life_2

Just read the prologue and you should be on your way. The core summarizes the plot well, but if you start clicking on links, you'll find way more detail than you'd expect to find from just playing the game.

In no particular order:

Useless and simple puzzles and LOTS of them(ex.Marvel Ultimate Alliance)

Disrespectful players (ex. any game on teh internetz)

Bad interface layouts. "Stop making me scroll past that useless ****ing key!"(ex. Oblivion (PC))

AI opponents that are harder because they cheat (extra health, bonus resources)(ex.Age of Empires 2)

Stutter glitches that usually occur during obnoxious noises (ex. Team Fortress 2)

Ridiculously long final levels. Fighting the same 5 enemies in the same looking environment for 2 hours while dangling the 'you're almost done' sign in front of you is not climatic, it's annoying! (ex. Dungeon Siege 2)

When the character you play as makes an obviously dumb choice. I call it sitcom TV syndrome. (ex. Final Fantasy X)

Choices without consequences, especially in dialogue. If I say something stupid or mean make it have an effect, don't loop back into the recycled dialogue. (ex. Oblivion and Marvel Ultimate Alliance)

Overcrowded HUDs that I can't turn off without seriously imparing gameplay. Seriously, I want to see the screen with the purdy stuff, not the lines and numbers the game is built on. (ex. Assassin's Creed radar)

Cliffhangers. Can't we just make a game without trying to turn into a franchise. You know with an ending! You know, I'm not even sure the gamehad a plot and Ididn't even realizeI was so much as close to the ending. (ex. Gears of War)

Oblivion! It has so much going for it, has so much potential, but it lacksvariety, or any reason to care about anything in the game world whatsoever. THE WORLD IS BEING INFESTED BY ZOMBIES...btw, feel free to loot the whole province, collect some plants, and watch a few guards get absolutey slaughtered like the idiots they are. It just could have gone so much farther by changing fairly simple things.

Oh and, making you do the exact same task 5+ times (with the same sub-plot) in a row that you've probably already done a couple tons for giggles should set off the boredeom alarms :(

I just want to be able to fail!!!

Scrap Metal Zone in Sonic the Hedgehog. Lets design an entire level that prevents you from doing the high speed run through that make the rest of the levels fun and then add spinning razor blades that travel faster then we'll let you move!

Then the factory type level at the end of Sonic the Hedgehog 2 made me want to bash my head in (###### mantii)

The introduction to Black and White 2. ***yawn*** but if you skip it, you miss out on things that help you later in the game.

In Streets of Rage 2 I hate the wrestling type boss found under the stadium. Perhaps I just need to figure out his weakness, but he breaks combos and is too risky to approach for throws

In Titan Quest I hate the Minoan Labrynth. Boring scenery, not very maze like design and boring enemies make for a boring area. In the expansion pack there is an area that is initally cool, but there are 5 levels of it and they're labelled 5 down to 1 so you know just how much torture you have left. Oh, and there are a whole 3 different kinds of enemies in that descent.

Bowser's castle in any of the MarioKart's. I'm just simply terrible at the sharp corners, unrailed edges and stomping blocks :(

World of Warcraft: Any of those areas that are desert like or deserted (except Tanaris) They just all seemed so alike after awhile :(

Dead Rising: The intro...lots of blah blah blah and locked off mall areas.

Which ever one finds that magic way to get the controls right. It may just be that it's really difficult to not look at an RTS interface on the PC whendesigning forthe console. Perhaps one of the developers will really break the mould in how RTS games are controlled that works perfectly with the controller. Tough part is they need a good game underneath that ;)

I'm keeping my eye on a SupCom port (due to my aging computer). Personally, the Halo universe has never interested me and I don't really know of any other RTS games coming out on the Xbox, although I'd really like to see many more!

Cliff Racers - Morrowind --mostly due to the afformentioned stuck on scenery so you can't save issue

Banshee/Ghost things - Oblivion --since I mostly played thief type characters, these things would take for bloody ever to kill and I'd have to resort to some mundane combat tactics for five minutes to kill one (my 5 pt fireball, YAY!)

Green Slime Hands - Kid Chamaleon --these things would jump at you, hold you, limit your jump and slowly kill you as you jumped around to shake it loose. Easy to kill if you hit the jump, but landing beside one after a big fall was treacherous.

Alien head on a chain - Streets of Rage 2 --that big bobbing head that just went back and forth on some sort of chain thing. You had to jump kick it, but due to poor 2D depth perception you'd normally land beside it and get knocked over. Just annoying because you don't even know wtf it is!

Flying Sentries - Bioshock --once you set off an alarm, two of these would follow you. Even when you killed one, another one would replace it. Extra annoying as it was usually accompanied by that god awful alarm noise.

Purple Catepillars - Sonic the Hedgehog --not so bad in the second game, but in the first one before the spin dash was introduced, these things were a pain to kill if you weren't in an area where you could not get much momentum. (Basically in a game about going fast, you almost always had to stop to navigate past one of these)