I've been using Synthesia on an old macbook air hooked to my digital piano on and off for a few years. It's really astonishing how quickly you can learn a song when you have instant feedback.
Although this tool is obviously not going to teach me dynamics and expression, I can't recommend it strongly enough for people looking to learn to play the piano by themselves.
Hmm, I tried Synthesia but found it unworkable. I have some basic skills at sight-reading and can play a bit by reading intervals. I found that this didn't work in Synthesia at all, and that I totally struggle to hit notes reliably. Combine this with the sheet music display in Synthesia being crap, and it got frustrating pretty quickly.
So I'm back to simply playing from sheet music. Feedback isn't a problem - you can hear when music sounds like shit pretty easily, and Synthesia isn't going to correct your technique mistakes anyway.
Comparing it to something like Rocksmith, I think I'm missing the display of where your hand should be anchored.
Although this tool is obviously not going to teach me dynamics and expression, I can't recommend it strongly enough for people looking to learn to play the piano by themselves.