Okay, I'm as surprised as you are. Obviously, I started watching this show because the Suze wanted to watch it. It was clearly conceived by the producers of American Idol as another way to cash in on the reality competition formula.
Audition shows where you get a "ticket to vegas" (instead of hollywood)? Check.
Vegas Week (instead of Hollywood Week), where the competition is whittled down to a top 20 (instead of a top 12)? Check
10 weeks of eliminations, losing a boy and a girl each week, until a champion is crowned? Check and check.
Fundamentally, there is nothing wrong with the formula, and this time they nailed it. And honestly? I think the producers themselves were a little surprised by the show they ended up with. So how did they get it right this time?
Instead of smarmy Ryan Seacrest, the show is hosted by the charmingly British (and leggy) Cat Deeley.

The auditions take place in awesome theaters instead of a cheesy room in a convention center.

The judges, except for the token brit (producer Nigel Lythgoe) are a rotating panel of talented dance choreographers that keeps the commentary fresh and interesting. This may not sound important until you've heard Randy Jackson tell another contestent that for me, for you, that was a little pitchy dawg.
But this is all window dressing. The real reason this show works is that good dancing is inherently watchable.
Without exception the people on this show are talented. The "bad" dancers are the ones that can only do one type of dance incredibly well; the show requires that you succeed in a whole range of styles. Oh, and did I forget to mention that girls who dance are all pretty much really attractive?
Look, it's summer. we all know the networks are going to be filling their schedules with unscripted programming, which usually gets a bad rap. But if they are going to do it anyway, we should at least take notice when one of these programs actually succeeds at entertaining us.