It's like learning to play songs by following along tablature which has been made to look like the scrolling icons from the Guitar Hero or Rock Band games. So it's far easier to pick up and play for beginners (compared to tab), and a fun diversion for experts. The 2014 version has a pretty cool improvisation mode where a backing band plays along to how you sound.
It's the kind of game where your mileage will vary depending on your skill level and dedication. For example I managed to learn "I Got Mine" by The Black Keys and "Take Me Out" by Franz Ferdinand to almost 100% completion, but ask me to play it without the game and I'd be hopeless!
In my opinion these games could use more blues songs that still sound good to play if you're solo, like Clapton, SRV and Hendrix.
Sounds reasonable, if you're supposed to be learning how to play the actual instrument, then more solo-type songs would be good but it's probably a bit harder for them to make them interesting in the game if there isn't other accompaniment.
I can play regular guitar and bass a little, I have real issue with electric guitar as my fingers are too fat to be able to fret individual strings, acoustic or bass is fine though, so might need an electric/acoustic.
I've got both Rocksmith and Rocksmith 2014 on Xbox 360, and I think it's terrific. I bought an electric guitar about 6 years ago but never really got around to learning how to play it. Rocksmith achieves the first step of learning, which is getting you to pick up the guitar and use it. Though I've been struggling to find the time recently to play any decent stretches of the game, I've really enjoyed what I've done so far. The Guitar Hero-esque elements help to keep interest and mask the sometimes monotonous side of practice.
One thing I've started doing is pausing the "game" progression in favour of intensive work on a single song. The song I chose is Jarvis Cocker's "Angela" because it's got a pretty simple and rythmic chorus. I've yet to master it at 100%, but I've learned how to play enough of the chorus that I could pick up a guitar and pick out the tune to a recognisable level. That's more than I've achieved without Rocksmith, so I take it as proof that it can work. There are some really good aspects like Riff Repeater, which lets you work on mastering a section up to 100%, slow it down to build up accuracy, or to stop every time you miss a note. Combining these three modes lets you work on a refine difficult sections without having to endlessly repeat sections you've already mastered.
The 2014 version makes some improvements (clearer note highway, easier navigation, stripped back functionality), but it doesn't have the "game" elements present in the first. I think you can also import the songs from the previous version for about $10USD, which gives you a total catalogue of over 100 songs, not including DLC. I haven't done this yet because I don't have a XBox Live Gold account, and I'm happy to play the songs in their own version for now.
There's quite a good blog by someone who has tracked his progression in the game since about 2012. He gets into a lot of detail, but I've found it useful to see how others are using the game. http://myrocksmithjourney.blogspot.co.nz/