The first Godfather is a perfect film imo; it's my third favorite film. It's also a film you have to watch in context to a certain degree. Dismissing it as another "by the numbers mob flick" is stupid because as TVC said, it's the original. This is like dismissing Straight Outta Compton as another "by the numbers gangsta rap album" - no, it's the original, and the innovator. IE, it's not the first of its kind, but it's the first defining achievement of the genre.
When I watch it I'm awed by how perfect everything is, without being stylistic or particularly show-y. The acting is amazing; every performance is top notch, even minor supportive roles. The score is classic. Many scenes are simply amazing - to me, the baptism scene towards the end stands out most. It's not a particularly heavy film in terms of content, but that doesn't mean it's simple. These are layered characters, some more complex than others. And then there's Michael.