I am a fan of music games. I have Guitar Hero World Tour, Metallica, 5, and Rock Band 2. I also bought Guitar Hero Smash Hits last year during Black Friday. I have played about 80 of the 90 something songs in Warriors of Rock, finished Quest Mode, and played online once.
-The Set List: This is entirely opinionated. If you are even considering buying this game, look up the full set list online. Personally, I think this is a great set list. It has songs I always wanted in a music game (ex. Nemesis, Burnin' for You). Beyond the songs I was excited to play from bands I either really liked (Rush, Styx, My Chemical Romance) or was at least somewhat familiar with (Queensryche, Night Ranger), the game also has songs which are funner than I expected. For instance, I originally had no expectation for Cherry Bomb, We're Not Gonna Take It, and Suffocated, but I love playing all of those songs. Overall, there are distinctly different songs which are more often than not fun to play. While there is a diverse set list, it is also more contained in the rock, alternative, metal, and punk genres (I thought GH5 was too broad).
-The Difficulty: In my opinion, the main games in the Guitar Hero series have decreased in difficulty. With Warriors of Rock, they bumped it back up. Between the Megadeth songs, Slayer, DragonForce, John 5, and Steve Vai, there are some good challenging songs. Even some of the earlier songs are hard to play like Burn and Call Me the Breeze.
-Importing Songs: Yes, there is a small fee to do this, but it is a thousand times better swapping discs or never playing songs again. You can import about half of the songs from WT and SH, about 80 songs from 5, and about 39 songs from Metallica. In fact, Activision waived the import fee for GH:M for the first week, so I didn't pay anything. If you have been a Guitar Hero fan for a few years, you probably have too many games on your shelve like me. When you import all of your games, your set list becomes impressive both in terms of bands and the scope of genres. The new features are updated automatically, so even the Death Magnetic album, which I got two years ago, has the new challenges found in Quickplay+. Speaking of which...
-Quickplay+: Remember those challenges from GH5? Remember the leveling system from GHWT? Those are combined together in the new quickplay mode. You can keep track of how good (or how bad) you are on a song easily. You can still save playlists and sort songs like in 5.
What's Not So Good/Bad:
-Some songs don't belong in a Guitar Hero game. Personally, I think Bohemian Rhapsody is one of the greatest songs ever written, but it should belong in Rock Band 3 and not WOR, since it has an actual keyboard. Instead you play the piano part with a guitar. Also, I really like Seven Nation Army and Uprising, but they aren't the most exciting song to play on guitar. Instead of making them the easiest songs in the game though, they charted the bass section too [QUICK EDIT: So apparently White Strips don't have a bassist, so you are actually playing the guitar part in the game, but you can still play as a bass guitarist in the game, so the same problem still exists]. I don't care if a chart is 100% accurate and I don't mind playing some synthesizer keyboard parts in songs, but it is a little distracting in this game.
-Quest Mode: I don't know why Acitivision and Neversoft hyped this at all. Quest Mode barely has a story. There are no over-the-top/epic rock moments. Instead we get bands playing at venues (just like every other game) who randomly transform into a monster. The transformations and power-ups are unnecessary, and make the game too easy. It is possible to have star power on, with a 36x multiplier for an entire song. However, you don't earn points in this mode. Instead you can earn up to 40 (yes 40) stars. The only cool moments in Quest Mode are 2112 and fighting The Beast. I doubt anybody is dying to play through Quest Mode, but just so you know, there is absolutely nothing to talk about. Personally, I would skip Quest Mode, except...
-Some songs are locked: Yeah. The last tier (the hardest songs in the game) is locked, so you have to play through Quest Mode in order to play every song. I believe you have to do this to unlock 2112 as well. You will only have to endure this once, and if you are experienced at Guitar Hero or Rock Band it should only take you about 6 hours to reach the end. Still, was a little annoying I could play Black Widow of La Porte when I first got the game. Oh well.
If you are not bored with Guitar Hero, then you should have some fun with this game. I picked this game over Rock Band 3 because I like this set list more, there is a lot of crossover with previous Guitar Hero games (RB3 has songs from GH 1, 2, 3, WT, 5, and WOR), and I don't want to budget for completely new instruments right now. So basically I picked this game, because I thought WOR has fun songs and on that front the game has delivered.
If you are just now thinking about playing a music game, pick up an earlier game (either GH5, Metallica, or RB2. I wouldn't go much earlier than that), since they are finally coming down in price.
QUICK EDIT (10/17/10):
Although I still believe the powers in Quest Mode don't add much to the game, I do have to admit something. In Quickplay+, you can select 2 powers out of the 8 in the game. The game doesn't save your score, so you don't have to worry about beating people who somehow got 2 million points on a song (you still see your score, but it only saves the stars you received). Overall, I think using power-ups in Quickplay+ is fun. Since you are able to pick which powers you use, it is better than Quest Mode, which either assigns random powers based on the rocker's set list, or you play with 4 or 8 powers which makes the game too easy. With that in mind, the powers still don't add anything new to the gameplay. They are simply a new gameplay mode. If anything, this only reinforces how fun Quickplay+ is.