The big question about a Jim Carrey film is 'is it one of his good ones?' Yes, his performance is commendable. He reins in the gurning and jerking to realistic levels, though he does play a ridiculously flamboyant hyper-intelligent lying nutcase, so the ground of realism is set pretty far up into the stratosphere of overacting. For me it worked OK. The film is based around him. He doesn't do that 'I am not gay I'm performing' thing that famous actors sometimes do.
Ewan McGregor plays his love interest. He's got a narrower compass than Jim Carrey, but gold charisma. I think he drew very much on Marilyn Monroe in putting the character together. I don't mean he does that breathy 'happy birth-day mister pres-i-dent' voice. But sexually alluring big-blue-eyed innocence. Like in Seven Year Itch when she says 'And there I was naked with a perfectly strange plumber!'
For example, imagine Marilyn as Ewan here:
Ewan: And the next guy I went out with was a real Broadway producer!
Jim: What was a Broadway producer doing in Miami Beach?
Ewan: He didn't say. And the next one was a full blooded Cherokee!
Jim: Oh really? What was his name?
Is it sexy? Well, it's fairly sexually explicit. You see Jim C fuck a guy (not Ewan) up the ass quite assertively. But on the whole it's more romantic than sexy. I'm not a great one for romance, but it was pretty sweet I thought. Not a film to set the world on fire, but a nice enough evening out, and with its heart in the right place.