Yep I agree with goodlife, actually rocket has been very bad this year. Mine went straight to flower before we even got to eat any of it! However if you let it flower and seed it produces abundant seed: I let it self seed actually and always have bits of rocket popping up, just a little goes a long way!
As the leaves get older they get tough and are not so nice to eat (very strong). I grew mizuna for the first time this year and I am rapt with it, it has grown like wildfire.