I really don't know if it really became that popular, but there are a few reasons for me to get psyched about the game.
For starters, it's being made by Splash Damage, the guys who made my all time favorite online fps, Wolfenstein: Enemy Territory, wich also happens to be 100% free. When TF2 got released, I really, really wanted to love it, but I just couldn't, I just kept going back to ET.
Don't get me wrong, I like TF2, but what made ET so special to me, aside that it was the very first FPS online I've ever played, is that every single level has multiple objectives, not like TF2 wich is a single objective per map. For example, Goldrush is a mode for TF2 while there's an entire map named Goldrush in ET, wich happens to be strikingly similar, but at the same time, completely different.
On TF2, Goldrush is about pushing and protecting a mine cart with explosives to reach it's destination, once the cart reaches it's destination, it's all over and the next map is loaded.
In ET, there are quite a few objectives to accomplish in that single map. First, you gotta secure a tank that's at the hands of the nazis, once it's secured, you have to escort it, similar to the mine cart in TF2, except that it has invisible rails and the tank can crush you if you are foolish enough to stand in it's path, also, it happens to have a mounted machine gun, so that you can immolate as many nazis as you can. You have to escort it to it's destination, wich it's some kind of bank, once you get there, the tank will shoot at the entrance doors, so you can steal some gold bars to a nearby truck, hence the name Goldrush. At this point, the game immediatly shifts from escorting to some kind of CTF (Capture The Flag). Once you get the gold bars in the truck, you gotta make one final push to get the truck outta the city. Once it's out, it's all over and the next map is loaded.
To me, ET is more of a "Team" game than TF2 itself.
So, what does all of this has to do with Brink?, as far as I've seen from videos and screenshots, this may be the legitimate spiritual sequel of Enemy Territory. Just look at it, the first time I played ET, I was completely lost, only to find by myself or asking other players where to go and what to do, while Brink will add an automatic wheel that can give you an objective, in theory, this will encourgae teamwork a lot more and many people will feel useful and won't get easily frustrated. Also, you just gotta love the whole "parkour" thing of moving nimbly wherever you want, not many games have done this before. Also, the whole thing of customizable weapons and even your very own look is quite neat.
I know Splash damage made Quake Wars too and while I don't consider it a failure, it didn't picked up as I hoped. Certainly, I'm more excited for Brink than for any other (FPS) game this year.
I've already pre-loaded the game on Steam and I'm eagerly waiting for monday to start playing.