Yes Man is a generic comedy to set up a gimmick. That's fine as long as the gimmick is good. This one is, so it doesn't matter that it's a guy named Carl Allen (they didn't even think of a surname) working in a bank with three friends. That's just common ground.
Review: Yes Man
The gimmick creates sets for Jim Carrey to be crazy. He's still at it, finding new ways to contort his body and twist his face. That's really the difference that makes any generic gimmick more entertaining than someone else's.
The movie explores all the no's and Carrey performs and makes it funny. The yeses are mostly safe. They're all demonstrable activities of course, but nothing really daring. There's an awkward, naughty one but it's still PG-13. There are montages full of visual gags.
There are some <B>Final Destination</b>-esque circumstances to push Carl when he tries to say no. That only happens twice though, so it's not really explored.
The banter is quirky in typical romantic comedy settings. At least they seem to acknowledge that it's free spirits meeting in contrived circumstances at predetermined points in time, so they keep it fun.
They also made sure to include corporate synergy. The film is heavy on Harry Potter and 300 references, all Warner Bros. properties. They did get some Saw footage in there from Lionsgate.
The overall idea that yes leads to good things is true spiritually. The film also shows how it's just not supposed to be literal. Just be aware of opportunities, but don't be blind.
The bad side is only one outrageous misunderstanding. There are no real consequences. That's a missed opportunity. Still, it's sweet and harmless.