Not considering any technical issues (lag, bad framerates, no sound, etc.) that people might have, I would say that the top issues in the PC version of Brink are (probably in this order):
1. The undesirable effects of the do-it-all use key, including accidentally performing unintended actions because you happen to be close to a certain player or object and having your movement controlled by the game at all. I think the first issue could be fixed by implementing a weapon/item bank and allowing for different types of actions to be binded to different keys. As for the game controlling your movement, I think that whatever benefits it might offer are greatly outweighed by the simple fact that it can often force you to look and move to places that you don’t want to look or move to just because you want to help your team out. And this can lead to annoying combat situations.
2. Lack of performance-friendly and competition-friendly customization options. In particular, you should be able to customize your HUD and video settings a lot more than you currently can.
3. Bad sound localization. The sound localization seems to be better in ET, which was made 8 years ago. In particular, I often find it hard to tell where gunshots are coming from, even when someone is shooting from just a few feet behind me. I also find it hard to hear footsteps and where exactly they are coming from.
4. No demo recording. This is especially important for competition, as it makes the detection of hackers much easier.
5. No first person spectating. It’s fun to be able to spectate your teammates after you die in first person because you are able to see what they see and how they are shooting or performing other actions.
6. Lack of manual voice chats. Not only did manual vsays add to the fun of playing ET and ET:QW, but they also helped players to coordinate their actions.
7. Bad in-game chat implementation. The global chat is the same color as the general info text, so it is easy to miss when people send a global message. Also, the width of the chat space is very small, making it somewhat awkward to read longer messages. Also, like many others have suggested, in-game chat should be allowed during the cinematics (which, by the way, players should be able to disable) and basically at all times when a player is connected to a server (besides when the map is loading). Making it hard for players to communicate via text chat during the game just takes away from the social aspect of the gaming experience and makes players feel somewhat disconnected from one another.
8. The obtrusiveness of the objective wheel. While not a HUGE issue, I do find it annoying that the wheel takes up the screen and forces me to do something with my mouse other than changing the orientation of my character. Maybe they could implement an objective menu similar to the vsay menus in ET, where you have to just press a certain combination of letters or numbers to pick which objective you want. That way you can keep looking where you want to look while you quickly pick an objective. Like someone said in another post, I can’t imagine that they would have designed the objective-picking system in this way if the game had been designed solely for PC.
9. Gun recoil, spread, and damage. This might be ranked higher on my list, but I don’t know all the facts yet. I have heard things like the spread of the guns is too random and too excessive, and I have kind of experienced this, but I need to pub more to really get a feel for any nuances with recoil and spread. I have noticed that iron sighting and crouching don’t really seem to help my accuracy much; I tend to get better results just by strafing and firing from the hip, which leaves me wondering if the gun/shooting system is perhaps flawed. The shooting does, in certain situations, certainly feel somewhat random, but maybe it is something that can be mastered…
10. Bad server browser filter system. It should be a lot easier to find the kind of server that you want to find.