One fear with a game that teaches you how to play guitar is that it is actually teaching you to play the game and not how to play the guitar in general. Happily Rocksmith solves this quite well.
As I have written before, the mechanic Rocksmith uses is to split each song into many phrases and you progress through the levels of each phrase independently. Obviously at some point your progress reaches a natural halt because you have reached the maximum level of every phrase in the song. You can actually do this without it ever having played the entire thing: using the “Riff Repeater” tool on each phrase until you have maxed it out.
Once you have maxed-out every phrase and scored over 100,000 points in a practice session or normal performance you are eligible to play the song in Master mode. In theory at this point you know the song and therefore no longer need to see the notes on-screen: Master mode hides them, and goes further in that it also conceals the song-progress indicator at the top of the screen. This leaves you with no visible cues as to where you are in the song, so you have to play close attention to the rest of the music. You also have no visible cues about your own playing accuracy: so you need to listen to yourself and judge your own pitch precision.
I first unlocked Master mode playing the Bass part of Pixies Where Is My Mind? I expected to perform quite badly when I first attempted it because my score on normal had only been about 103,000 points: I was pleasantly surprised to get over 166,000 points. You get double points in Master mode, so I lost about 20% compared to when I could see what I was doing: not perfect, but I was expecting worse. Some of that loss can probably be put down to the unfamiliarity of the experience: I shall try and remember to report back on my initial losses the next time I get a song into master mode.
Buoyed by this initial success I thought I should go after the 200,000 points milestone: partly because there is a trophy for it and partly because it would mean I could play it unseeing about as well as I could play it with the visual cues. It took me three more attempts to achieve this goal. Between attempts Rocksmith replays your performance along with the visual cues you would see in non-master-mode, so you can get some useful hints of where you’re dropping points from that. I didn’t replay in non-master-mode at any point.
I was playing on fretless bass and was very concerned that I would drift away from the correct notes and, absent the visual cues, never get back: in actuality this didn’t happen; partly because I was listening more carefully, but mostly I suspect because the absence of information on-screen lets you use your eyes to check where your hands are without missing anything. If anything my pitching was better in Master mode than in normal mode.
So what do I conclude from all this? Master mode is a good continuation of the game into a more realistic performance scenario. I think it is introduced at the right time: the criteria to unlock it are where you have learnt it quite well but long before you are a virtuoso. I imagine it would be a lot more difficult if your part included the first note (or the first note after any extended period of monotony or silence); the situation doesn’t arise on the song I performed so this is only speculation.