Great, but has untapped potential.
The story is great. The Security vs. Resistence storyline was very unique, in that the developers actually tried hard to create a more true-to-life feeling of the game's morality. The game breaks away from the tired "good guys vs bad terrorists" plot of almost every shooter, and instead makes the motivations and actions of each side greatly understandable. It's obvious a lot of work went into the story, but I would have liked to see more of a true single-player, story-based mode with fleshed out characters.
Gameplay is incredibly fun. All of the weapons are balanced to an good degree, and they all handle with unique characteristics. Each weapon feels like it has it's own personality, which is something hard to create in games. Each feels like it has a rich history behind it when you look a the different models. The gameplay is very arcade-like, shattering the mold of "realistic" first person shooters. Instead of being based on "who can hit first, wins", the game flawlessly combines movement with shooting, and both are extremely important to succeed.
Movement is something that has been payed great attention to with the SMART movement system. Parkour feels very natural and intuitive, yet it does have a layer of complexity. For some players, it's a route from A -> B, for other players, it wins games. It really depends on how you want to play, and brink gives you a lot of freedom in that regard. The character customization and unique art and music styles really give the game a different appearance. It's colourful, unique, and how many shooters can you really say that about these days?
There are issues. Iron sights seem like an afterthought, they aren't very useful at all on most weapons. Some classes, like the Medic and Engineer, gain points much faster than others like the Operative and Soldier. There are 3 body types to use, but most people only use Medium or Light, because movement is such a game-changing factor. Story is rich with potential, but it remains untapped. Singleplayer feels like a last minute addition, being comprised of only multiplayer with braindead bots. Some missions are biased towards a defender winning
Overall, I say people should buy and try Brink, especially if it is on sale. It has it's flaws, yes, but it has potential and I would encourage supporting the studio behind it so they can release that potential.