I figured that I might as well do more than a single post on this one, so here goes.
10. Box-stacking. Just because you can do box-stacking puzzles where the boxes seem to be covered in Vaseline doesn't mean that you should.
9. Excessively narrow catwalks. Your character runs by default and when he stops, he slides for quite a bit. However, massive sections of the game require that you not only crouch and crawl along, but that you crawl along a beam or edge about the size of a 2x4. Several times, the beam you are to crawl along is lost in the background rubble. For example, near the end of the game, your teammates are screaming "Run to the horse, Gordon!" You can see the horse, but the way to get to the horse is obscured by what remains of a cement wall. The only way to see the beam you have to traverse is to go to your teammates, turn to your right and look down. Even then, it's a three-part beam. Why couldn't I just knock down a wall and go out? Don't even get me started on the bridge level...
8. Load times. When it takes longer to load a level than it does for me to boot Windows, you know it's bad. I probably spent 20% of my time loading. One time, the game crashed during a level load. I didn't even notice until five minutes later.
7. The "stutter." The audio/video stutters were insane. Even when I reduced my texture resolution and dropped my sound to two channel, I'd still have period of up to 30 seconds where the frame rate would drop down to .5fps and the sound would stutter. Inexcusable.
6. Requiring media for the retail product after Steam account association. Sure, after I associate my account, I can uninstall the game and download it again from your highly congested servers and spend 36 hours saturating my pipe for no good reason, but why would I want to?
5. Too many "guess what the designer had in mind" moments. Oh, the designer wanted me to stack a box so that I could jump up onto this ledge before getting crushed by this section of wall that I've never seen move before? Oh, the designer wanted me to use the hanging casket so I can go on a four-minute ride that is somehow less entertaining than the "It's a Small World" ride at Disneyland? Did these guys never play "Deus Ex?"
4. Incomplete and poorly implemented closed captioning. Don't get me wrong. I applaud the Valve guys for going through the effort to implement closed captioning for this title. However, there were several areas where the subtitles would not appear for dialog. There were also several areas where there was so much happening in a small section that massive chunks of dialog would scroll past before you could finish reading them. Great idea...hope they get it right for "Half-Life 3."
3. The flashlight. Let me see if I get this right...they've been improving Gordon's suit for years, integrating dash capabilities, improving the HUD, etc., etc., but running a cheap shoulder-mounted flashlight uses as much juice as doubling your run speed or generating additional oxygen for when you're swimming?
2. The rest of the NPC's. The care that went into the modelling of the primary NPC's simply throws the lack of work done on the rest into sharp relief. While Alyx and Barney look amazing, most of the rest of the NPC's just don't show the same amount of care.
1. The ending. They build you up for a Bruckheimer-style dash to safety, but end up dropping you into a black storage unit until you're needed again? The more I think about this ending, the more pissed I get.