The build of the game I got to play was alpha, although it was pretty slick and I didn't experience any issues. Ubisoft tell me that there will be a closed beta coming up later in the year before the game gets a final release. Personally I can't wait as it was a lot of fun.
It's classic Assassin's Creed III gameplay - going from mission to mission, fighting, killing, rescuing and getting that bit closer to the Mad King. This whole part is set in the Frontier, so will seem familiar, but different.
A lot of people really loved, and still love Guitar Hero, and for those people who would like to take their guitar playing to the next level, or rather learn how to play the guitar for real, then Rocksmith is certainly something that could help with that.