It all sounds a little on the dull side, but it's the slow progression of events and the gradual way we get to know the characters that actually makes the film so enjoyable. Spacey is excellent in playing the role on a knife edge between believable alien and hopeless delusional and Jeff Bridges provides his usual gruff performance but actually appears to develop as the story evolves. Barring a slightly suspect bluebird, there are no special effects, space ships or CGI aliens, but the film maintains an otherworldly atmosphere through the script alone, which can only be a good thing.
Whether you're into sc-fi, mystery or human drama there should be something in K-PAX for you to enjoy and appreciate. It's got to be one of the most underrated science fiction films of this century and the 'Spacey factor' takes it to a whole new level. It's not quite a 10/10 but it's close, so it is possible to 'beat a bit of Spacey' but only just.
If you like this you could also try:
The Life of David Gale, Starman, Contact.