If you don't have plans to see this movie, you can check the spoilers here and then come back.
About 15 minutes in, I was concerned Limitless would be a movie that coasts on a decent premise--a super drug that unlocks 100% brain capacity--and the charm of Bradley Cooper, and while it does have its flaws, it's not lazy, picking up considerably once the story gets rolling. The plot is not the most linear (not that every plot needs to be, but this one has crazy elements that would have stood out more had the bulk been a bit more mundane), but it's not boring and the questions raised about the drug and the power structure behind everything keep things rolling even if it occasionally trips over the byzantine complexity it wants to have. I wish they would have delved deeper into the moral stuff (Is the person you become on the drug still you?), but it's not a glaring loss. The script doesn't produce a slew of memorable lines, but it gets the job done. The real standout element of the film is the visual effects, the way director Neil Burger uses things as simple as shifting the color palette to communicate use of the drug to pulling in gonzo effects to show thought process and movement; this was probably my favorite part of the movie. Bradley Cooper doesn't disappoint in his performance to the point it took me the whole length of the movie to realize his character isn't really the type I was sure I wanted to root for and by then the credits were rolling. Abbie Cornish is fairly awful as his love interest and Robert De Niro is a parody of himself as his mentor, but it's really the Bradley Cooper show, so it's not that important. The best of the supporting cast are Anna Friel from Pushing Daisies as his idealized ex-wife and especially Welsh actor Andrew Howard as a Russian thug who also gets on the drug. The movie probably didn't need to be an hour and 45 minutes, but again, it's not bad; I wouldn't go out of your way to track it down, but if the hooks intrigue you or you're a Bradley Cooper completist, I think you'll enjoy it.