At one time this show was the fastest growing on TV, and now, it is pretty much over with the story, but it still airs, and it is awsome. They do a good job at keeping the same plot running without getting boring (some seasons are all one plot), and it always is delivering something new (although the villains all try the same things normally). The comedy was well done too, and they didn't go overboard to get you to laugh, just went along with the characters moods (which are lifelike) and went from there.
Violence, while present, isn't the point of the show. Generally it is how Sonic and his friends get along on earth, but the final season is pretty violent (and scary at times).
Other than that, there is nothing to worry about except that maybe you wont like the fact that Knuckles and Amy loose their tempers a lot, but that is made up for by the family values supported at times. It also stresses friendship at the same time, and the characters can normally work as a team, except Sonic and Knuckles settle disputes by fighting.
Overall this is a great show. Sure the last few episodes weren't all that great as they went overboard in trying to keep it going, but it was good (the final episode was awsome), and this can be watched by anyone, and everyone can enjoy it.