See part 2. It's on the same scale as the original, I'd say.
Part 3 is pretty good. While the others are a solid 10/10, this ones more of a 7.5/10, regardless, it puts a good ending on the saga. If you have trouble finding any of them to watch, many people upload popular movies to youtube, though I havent checked for the godfather. Also, if you liked goodfellas, watch mean streets.