Better than Strangelove
This is a great movie if considered apart from the book.
I have not read the book, so I had no preconceived notions going in.
This is a great movie in its own right.
At the time of this writing, Dr. Strangelove is #13 on IMDb's top movies list.
If you consider that movie to be great, I don't know how you couldn't feel the same about Catch-22, because it has all the same great elements (dark satire about war, absurd intellectual comedy, beautiful cinematography, great acting from an incredible cast, great screenplay) plus a few extras (in color, more epic, snappier funnier dialogue). Unless you're just a big fan of actors playing multiple roles, in which case go rent Goldmember.
The only reason why I can imagine that this movie is not so highly rated is a natural, if unfair, comparison with the book, and the fact that Dr. Strangelove has about 20 times the number of votes, which means Catch-22 is sorely underviewed and underrated, in my opinion.