I usually loathe those 'the book was better' whiners, but I will say that the Fletch character is WAY cooler in the books, and what you see in the movie is basically Chevy Chase being Chevy Chase. I enjoyed that movie well enough at the time, and we all quoted lines constantly for several months but I can't imagine I'd really be able to sit through it now. All the other guys in the movie are basically there for Chevy to bounce jokes and insults off of.
FLETCH (the movie) still holds up. It's been years since I read the books but I remember thinking the movie was a pretty faithful adaptation, albeit a little more on the slapstick side. Then again I also saw the movie before I got into the books.
I'd be interested to see some kind of FLETCH reimagining. Maybe a TV show.