The negative reviews tell you why it's good.

Rating: 9/10 (23 April 2013)

Rango is a great kids' movie that plays on many levels, like all great kids' movies. About a hundred churchies here don't like it; that tells you it's realistic and morally complex. (One person complained about its metaphors for good and evil, because "many people take God and Satan seriously". Yeah, but we don't all think we hold a copyright on them.) And some folks helicoptered in to complain that it's violent and would scare some kids. Fifty years ago my parents took me to see Bambi and it scared me. So did Dumbo. It's vital that kids learn about fear, danger, and violence, and a cartoon is the softest place to do it. Thank God my folks understood that. For the record, Rango's violence is funny and completely unrealistic. Would it kill you to talk to your own kids about the difference between slapstick and the real world?
There are "swear words" here, if you still think "hell" and "damn" are swear words, because it's a gritty Western. (That happens to star a chameleon.) There are a lot of Hispanic references and characters, because Hispanics invented cowboys and the "American" West; Nickelodeon simply decided to unwhite-ify the Hollywood version, for a change. (The guy I read who complained about that wasn't even Hispanic. Meanwhile, I have Hispanic friends who love this movie, in part because they're in it, for once)
There are several stereotypes, ethnic and otherwise, because it's a satire. If you can't grasp irony, avoid this movie. In fact, never go outside. And several minor characters smoke. I hate smoking. But: stereotypes, remember? Westerns? Cultural memes? How about just teaching kids the difference between allegory and real life?
As for the moral content, the "lessons" of Rango, which, I think I can state without incurring a spoiler slap, are: 1. the world is a crazy place, 2. scary problems have to be solved by ordinary people, and 3. a quick wit and a lot of luck sometimes beats a quick draw and a lot of money.
If you agree with that, and aren't scared of your own shadow, see the movie. I loved it, and I'm hard to please. It's a great romp, a witty farce, and a lot of fun, precisely because Nickelodeon didn't sugar it down to pious drek.