I loved Brink, it was definitely nice to get out of the cookie-cutter FPS games. But there were MANY things lacking and some things were just plain bad. I think these things would put a large improvement on Brink 2 (if it happens).
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1. A better campaign. I for one am not that centered around campaign. They're usually just a warm up introducing me to how to actually play the game. I'm mostly in it for the gameplay. But this game's campaign was pretty much a joke. The story was amazing, and had a lot of potential, but the actual cutscenes were horrible. I'm sure if they tried they could definitely improve the quality of the animation. The way the missions were carried out didn't feel right at all. They all felt like mashed together Freeplay missions. Granted, it was fun, but I'm looking for a more cinematic, unforgettable experience. It mostly just felt rushed.

2. Customization. This game had great customization and was one of the main reasons I bought it. But no matter what I did, it still felt like the game was choosing for me. I'm glad they put this feature in because I loved it and never would have got to this point otherwise. They need to make then creation system more complex and personal. For instance, changing the color of your eyes, or the length of the bridge of your nose. Still keep the same style, just add alot more possible uniqueness and obtainable items. But of course keeping the same awesome style they had.

3. AI. This is one of my main issues. To put icing on the cake, the AI is horrible. To be fairly honest, they're a flaming bag of crap. Just improve the AI's competence and ability to prioritize objectives. This game is supposed to be a team effort, but I had a hard time finishing some of the campaign missions because I was trying to fulfill all the objectives at once while the AI would sit around chasing their own tails. Unquestionably needs to be fixed.

4. More content. My main problem with the game. I loved this game for it's originality, but it honestly got really boring really fast. I finished both campaigns and unlocked every item and ability within 3 days. The game definitely needs more weapons (with different effects and sounds), more outfits, more unlockables and more playtime. If this game had a lot more time and possibilities to offer, I would be satisfied for a good year.