It is my belief that this will teach you to play guitar. I've been fooling around with my guitars on and off for the past few years. I've learned a few chords and can play the first few bars off of tab for a few easy songs. I've never stuck with it long enough to be any good at all. One of the reasons is that it's hard to dedicate hours a day to practice when you are starting out. It takes a ton of work to go from making noise to making "music". It's demotivating and frustrating.
I've been playing Rocksmith for about a month now. I dedicate as much time to it as I possibly can, and wish I could find more. It's great because it works like guitar karaoke. The lyrics, bass, and drums are all there and you fill in your guitar part. I'm still not good, and I didn't expect to be after a month, but for the first time in my life I've played songs from beginning to end (even if I'm only playing half the notes or so). It's a really good feeling and has me more motivated to stick with it more than ever.
It's well worth $50. It's well worth msrp even. I took (group) lessons for I think about 8 weeks at a community college. I've learned just as much if not more in my month with Rocksmith and have enjoyed myself way more.