He is an excellent drummer - I interviewed him for 'Drummer' magazine years ago, and he really knows a lot about the art of not just drumming, but all levels of percussion from all over the world.
Playing slightly behind the beat - as Fleetwood does, gives the music a delicious tension which is very difficult to pull off, unless it is natural, which in his case, it is.
Just because he doesn't play with flash and bash, you should never underestimate his skill and timing.
Just listen to the 'Formula One' section of 'The Chain'. Ignore MvVie's bassline and just hear those tomtoms creeping up with Buckingham's guitar, every one right onm the beat and slightly lounder tham the last until he hits a crash cymbal and the vocals and guitar chime together. Skill like that is hard to find.