As of writing this I have about 20 achievements, probably about 20 hours(though the TA time is still listed at 11, but that will probably update.) I have all the main rock bands and guitar heroes and am fairly familiar with the genre.
I have the one guitar pack, so you start by plugging the dongle in and syncing the guitar to it. I noticed that the syncing works better direct vs through an unpowered usb hub, but once synced, it works fine from the usb hub. It worked well, I had no issues with either dashboard.
The guitar is 3 black buttons and 3 white buttons. Once you get used to it, it almost felt like they could have thrown in another set of buttons. It provides a reasonable challenge, but I don't think the learning curve is as steep as the 5 button controllers of the older guitar heros.
If you weren't aware, you can sing along with a mic, but there is no support for drums or bass(at least with one guitar). While I can see in the 'live' portion why drums wouldn't have been as exciting, I would have enjoyed drums being part of the game. It is also notable that your back library of songs does not carry forwards, so hold on to your 360 if you want to play them and don't want to wait for them to pop up in Guitar Hero TV.
Basically there is two main modes. Guitar Hero TV and Guitar Hero Live.
Guitar Hero Live is like the 'campaign' but this is also where you find the quick play for the on disk songs.
For the campaign, it is similar to past guitar heroes except you are picking from a festival chart instead of posters. You are presented with two festivals, and within each are several shows to pick from. The later shows in the festival are locked until you do x shows or sets. Doing sets also unlocks songs in quick play, so do that before you have a party or whatever. There didn't seem to be too much of a venue build up, you are apparently very famous to begin with based on the crowds. There is no boss type of deals, and I didn't find the difficulty ramp significantly as I advanced through the venues, at least not on regular difficulty. For some reason, I just find the three button part easier.
The sets are with different bands done in a live first person perspective. I thought it was kind of cool at first but you are really looking at your lane more than anything. In all honesty it reminds me a lot of sports video game crowds because even though they are real people, there is little things that seemed off to me at least.
When I glanced up and saw signs they were usually pretty large generic patronizing signs that didn't seem natural and mostly cheesy. I also thought to myself how the clothing of the crowd for the most part looked fairly neutral vs a sea of band related shirts like I have seen at most shows I have been to(You know the thousands of usually black shirts that most bands sell for 40 a pop that are near the entrances of venues). The other thing I noticed was the air looked noticeably really clean(smoke free) vs most shows I have seen. It also felt like I got nodded at an awful lot by my fellow musicians, I will have to watch for that next time I go to a show. The attention was almost too much in my mind, it would seem like it would have felt more real to give the singer more attention, then shift it for solos etc. I do appreciate what they were doing to create the Rockstar fantasy but I found myself wanting to go back to guitar hero tv because I liked the rock videos better because I wasn't rolling my eyes as much, The thousands of fans screaming at you or getting mad(they get mad quickly) was cool though. I didn't notice a mosh or anything on the faster songs though there is a couple crowd surfers.
The other main mode is Guitar Hero TV which is like watching MTV(when it had videos) and you just play with whatever is playing at the time. It has two channels you can pick from and it lists their programs like from this time to this time its metal half hour, on pop hour etc. It doesn't pause, you just play. It plops in a chart on the side with other players doing the same song so you can try to place ahead of them. The repetition of songs wasn't terrible but there are some songs that come up much more often than others. At the beginning of each song you can pick a hero power for that song, there are some that run out and you have spend in game money for. I liked this mode, it was fun seeing where you wound up on the chart of players it plots you against.
There is also a quick play area for guitar hero tv where you can use quick plays you earn to play whatever song you want, or you can spend some real money(6 bucks) for 24 hours all access. You are sometime given quickplays on levelling, but you can also buy quickplays from in game money you earn or you can use hero cash(which is game money you buy with real money). I didn't find a need to buy quick plays so far, it seems to give you plenty.
In addition to the two channels in guitar hero tv, there is an area called guitar hero premium where it will have a specific set of songs that you can earn bonus rewards for playing. To play a premium show you can either use hero cash or meet the criteria for the show. The criteria doesn't seem too difficult, play three specific songs and get 3 stars on each type of deal. I used some my of free quick plays to unlock them. I got the feeling when I tried the premium shows, to really earn the rewards you have to play on expert since it wants you place first to earn stuff.
Overall the game is a nice refresh to the franchise without straying terribly far. The Live aspect is alright, but the TV portion is the highlight in my opinion. The career seemed short compared to some past titles, but the game is fun. Some of the achievements may get tough once people on guitar hero tv start getting really good. I would say 4.5 is a fair score, it accomplishes what it is looking to do and provides a fair replay value.