Pretty Dull and Sloppy
Yes, there are a few good scenes but the film is a waste of time. Gene Hackman played his dull character too well and the plot itself had too many holes covered by the usual "Was he hallucinating??/Is there really a bug?/Was Duvall really murdered?/Was it all a dream????" crap.
Blow-up was a much better film. The Conversation is a Coppola misfire, although not as bad as One From The Heart.
As for all the multiple theories about where the bug is at the end of the film, get over it. Coppola himself doesn't know or likely care.