In terms of MMOs I've quit the fastest, Mechwarrior Online probably ranks #2.
1. LOTRO. I reached level 4, in a couple hours, then quit because I hated the combat and level-up systems, which were just like City of Heroes, which I also couldn't stand, although LOTRO at least seemed to not have incredibly boring intro quests like CoH did. If I don't have control over combat, I'm not going to play it (although this was not a concrete opinion until I realized I hated it while trying LOTRO). (DCUO and STO both have ability bars, STO having a crazy number of mappable abilities, but both give you direct control of your weapons on the ground instead of going "durr autoattack")
2. MWO. Played probably four battles with trial mechs and four battles with actual mechs. Then quit and haven't gone back. A large part of it was the insane repair costs. Another part was that the rewards for failure (one million dollars?) made no sense until you saw the insane repair costs, and then you realized they were just trying to keep people afloat (and failing, apparently, as the first battle with the first mech I bought resulted in 4.6m credits or so in repair costs, and there was no way to practice with your mechs or set them up beforehand). I played a few more matches with several other mechs before deciding that it was wasn't something I wanted to play, as there was no feeling of fun, just a feeling of dread when playing it ("Oh god, am I going to get killed again because I don't know what I'm doing, and then the team will lose the game and lose huge amounts of money and maybe have their mechs disabled because I'm a noob?"). Doesn't help that it threw newbies in against experienced players running in squads (this happened in my first game with a real mech).
3. Firefall. I played about 6 hours of it. I can see skinner boxes.
So... Hawken... Are you under an NDA or can you talk about it?