Great improvements, but a disappointing setlist.
The new keyboard feature is incredibly fun. While learning how to actually play a song may not be very appealing to the less patient folks, the game allows you to play the keyboard part on a guitar once you play a certain amount of songs on guitar, which is a great design aspect. My only complaint about keys is that some of the songs have disappointing charts, such as "Before I Forget" and "Need You Tonight." Though there are still fantastic song choices for keys such as "Bohemian Rhapsody" and "Cold as Ice."
I'm not so sure pro guitar mode was a good idea. It is a pretty hefty investment for someone to buy an expensive guitar compatible with the game to learn how to play. Not many parents will want to do this for their child. Also, how many people would want to say that they learned how to play an instrument by playing Rock Band? The music game industry isn't exactly looked well upon by a lot of musicians (ex: "Get a life!/Play a real guitar!"). I've never played pro guitar or bass so I can't judge it on how fun it is.
All the classic non-pro instruments --guitar, bass, drums, vocals-- work exactly how you'd expect, with some minor improvements to each. Guitar has the edition of trill lanes which are supposed to make playing a really fast trill easier, but actually make it harder, due to some strumming issues. There is also a tremolo lane feature, which can make fast and random strum sections easier, but can also screw you over a lot. Drums have the edition of pro mode which allows you to play cymbals separate from toms. Drums also have a feature similar to the trill and tremolo lanes, except with rolls. Like the ones on guitar, these can also pretty easily screw you up for no reason. Bass has the same additions as guitar, obviously, but now has the ability to have bass solos, though there aren't many. Vocals also has a few improvements. The talky sections now cover the entire vocals track and the arrow is visible during the talky parts. This is a great improvement, as you can prepare for the next pitched phrase, which was not possible in Rock Band 2.
The lack of a real career mode, which was pretty fun in Rock Band 1 and 2, is disappointing. All there is is a short amount of "Road Challenges" which consists of playing a group of songs at some location while your band is on tour. You can either select certain songs with limitations on your song choices (specific genre, decade, difficulty, etc.) or a random selection of songs, usually with some limitations as well. There are also some challenges, such as keeping a streak or using overdrive a lot, which adds a little to the fun. The Road Challenges are pretty entertaining, but they can literally be beaten 100% in a couple hours. Band Tour in Rock Band 2 took me weeks to months to complete, and not even to 100%. This is obviously not the most important aspect of the game, but it is still disappointing nonetheless.
By far the most disappointing aspect is the setlist itself. There are some great song choices for the game, especially with the additions of keys and harmonies, such as "Bohemian Rhapsody" and "Roundabout" but some songs just seem worthless for Rock Band, either because they are incredibly dull to play on every instrument ("Killing Loneliness") or not recognizable and/or memorable ("King George" doesn't stand out, either musically or in gameplay). Their seems to be a distinct lack of difficulty in this game as well. On drums, "Llama," "Roundabout," "Caught in a Mosh," and "Beast and the Harlot" are the only songs that provide a reasonable challenge for a good drummer. This is compared to RB2's "Visions," "Shoulder to the Plow," "Panic Attack," "Battery." It is similar on the other instruments as well. There is also a lack of heavy metal in this game ("Foolin'" and "Here I Go Again" do not count). The heaviest tracks are arguably "Caught in a Mosh," "Before I Forget," and "Beast and the Harlot." But if you tell a metal fan that these are the heaviest metal in the game he/she will be pretty disappointed. Rock Band 2 had "Peace Sells," "Shoulder to the Plow," "Souls of Black," "Panic Attack," and several others. I'm not asking for the setlist to be entirely metal or even mostly metal. I just wish there was at least some heavier stuff. I'm sure not many would be disappointed if they replaced "Outer Space" with a heavier song. It would at least increase the overall difficulty of the game.
Speaking of difficulty, the difficulty tiers are beyond messed up in Rock Band 3. There were a few oddities in previous games ("Lump" and it's tier 5 drums...), but it seems Harmonix just threw a dart at a target with the tiers on the target. I'm not exaggerating at all. "The Beautiful People," "Something Bigger, Something Brighter," "Killing Loneliness," "Sister Christian," Cold as Ice," and many others have outstanding tiering issues. The most laughably bad one is the bass tier for "Jerry was a Race Car Driver." How in the name of all that is holy is this not in the impossible tier when "The Look" is? It's seriously one of, if not the hardest bass songs in the game. The Look is just slow strumming with little to no fretting. This is just a nitpicky argument, but I'm OCD so I care about these things.
Even though the setlist disappointed me, it's still a Rock Band game, and therefore there is a lot of fun to be had here. It's even more of a must have at parties than previous games because of the new instruments.