When I first saw The Godfather years ago I was disappointed and bored, expecting an exciting and pacy gangster movie. But when I watched it last night I enjoyed it. Maybe I'm more mature. Yes, it is a good movie, with an involving plot and a smouldering tension, but it depends what you're looking for. As for Godfather II, I've never seen it.
Personal opinion in films is a hard thing to gauge.....it's hard to say that you will like one sort of film because you have liked others and so on...but when in doubt about anything to do with films then I go to http://www.imdb.com
the internet home of the movies...if you click on this link http://www.imdb.com/top_250_films
you'll see that the come in at 1 & 3 on the list split by "The Shawshank Redemption"...must be something good about them then eh?