Neither reinvent themselves, and there are some forced cheesy moments (what romantic comedy doesn't).
What made the film work for me was Grant's delivery of his lines. He's got excellent comedic timing. Also:
If you're going to see this film, chances are you are a fan of one of the principles and also of romantic comedies. If that is the case, I think you'll like it. A pretty good romantic comedy: B-.
If you lived through the eighties (especially if you're between 30-40 years old and so were "plugged in" to pop culture in that decade) you might want to up the grade to a B/B+. I did, and found it to be a lot funnier perhaps than others not in that demographic.