First impressions are that it's a step up from Guitar Hero: World Tour but I still prefer the Rock Band franchise over the Guitar Hero one. Some of that is just a preference about the graphical style - I'm not fond of the round blobby notes, nor the more cartoony style. Some of it is that I find the in-song UI harder to read at a glance in the GH games. Of course familiarity would make that easier - but even once you account for that I still think it's harder to spot how well other band members are doing, and hard to spot if they have enough star power to activate. It feels like the game thinks I should be worrying more about how I'm doing and not caring so much about how the band is doing, and the way the game mechanics are that's probably deliberate. It feels like there's less interaction between players - if I activate star power, that only affects me, unlike overdrive in a Rock Band game. And the things that do affect the whole band mostly depend on playing your own part well, the only exception is you get even better band bonuses if you all activate star power at once.
We played a few hours of the career mode - which is a pretty linear affair, but given more replay value with the "challenge" for each track. At first you only have one venue & a small handful of songs in that one open, and as you earn stars you open up more venues & more tracks in each venue. I think we finished up a couple of venues last night & had half a dozen open to us with quite a lot of stuff still locked. Each "gig" is a single track and the vast majority are a specific single track. You can get up to 5 stars on the track (like normal) and then up to 3 more stars if you manage to do the challenge for the track. These vary - one track might have a guitar challenge to use the whammy bar for a certain number of seconds over the whole track, another might have a drum challenge to hit a certain number of the kick pedal notes. Or a whole band challenge to have a band multiplier of 2 or more for so many seconds. Some just happen if you can play the track (like all the drum ones so far), some require playing a bit different (most of the guitar ones so far ;) ). So that gives each track a bit of replay value. The last 2 or so gigs in each venue have been "pick a song" ones, with a specific challenge (like play lots of chords on the guitar) so you choose your song based on that. As well as giving you extra stars the challenges also unlock things like costumes.
The challenges per track are one of the things I particularly liked, the other is one of the details of the charting for the guitar (which was in GH:WT so it's not an innovation, but I'd forgotten about it). There are passages where you hold down one note & then play other bits & pieces while it's sustained. Which is a genuine musical thing that they've added to these games that RB doesn't have, surprisingly. (ETA: Also - open notes on the bass, which I'd forgotten about until some came along in my lunchtime gaming session ;) )
So, so far it's well worth renting & it fits in nicely - we finished up with Lego Rock Band at the weekend & Rock Band 3 isn't out for a few months. But still, I think it falls into the "good to rent" category as I don't think I'll be coming back to it long term like I have done with all the Rock Band games we've got.