AGAIG is a film featuring Jack Nicholson as an extremely obsessive character but one that is, unusually, not particularly sexual. Now Mr N does "maniacal" with natural ability, but it must be said that he does pathetic obsessive in this film very well also. The other players, including the delicious Helen Hunt, do very acceptable jobs, but their parts are not so intriguing or demanding.
That said, the movie really becomes nothing more than another quirky romance with amusing characters of variable credibility, and a few scenes, chiefly predicated on Nicholson's foibles such as an obsessive unwillingness to step on a crack, that amuse in the Hollywood way. There are a few lovely moments---the compliment Nicholson pays to Hunt in the restaurant is inspired, and the response from Hunt and her mother to the doctor when he visits and proffers a business card complete with his home phone number says volumes---but these do not a memorable cinematic event make.
The plot is not worthy of detail, but is comprised by a series of scenes during which Hunt, a waitress and mother of a sick child, who works in one of the few restaurants in NY that will tolerate Nicholson, and Nicholson, an apparently successful writer of sticky romances who lives a hermit-like existence with his numerous obsessive traits, get to know each other over the course of a few weeks, and eventually strike up a relationship.
About 5/10 with an 8/10 for Nicholson's portrayal.