So, Rocksmith 2014. Well, it's basically the original Rocksmith all over again, but basically better in every aspect.
If you don't know about Rocksmith, let it be told that Rocksmith (2014) is actually the best serious game known to me. It is played with a real electrical (bass) guitar (not included), using an unfortunately proprietary audio-jack-to-USB cable (only included in retail boxes), which does an excellent job at putting your guitar audio through to the game.

The primary goal of the game is for the player to learn to play (bass) guitar hands-on. For beginners the game offers some lessons teaching the basic technique, and there are so-called "guitarcade" minigames that basically gamify typical guitar exercises, focussing on repition for memorization.

And then there's the actual "meat" of the game, playing songs that you likely know at least a good deal of if you're into any kind of music involving electric guitars. This is the part that probably even somewhat more experienced guitar players can enjoy, because, well, the game teaches you to play these actual songs. If you should ever find that too boring (which I doubt, because the devs are still maintaining the game and pushing out another bundle of usually at least three songs every other week), you can also go and do some improvising with the built-in "jam session" mode.

To be fair, the latter is relatively basic and really mostly expects you to play lead, but you can mix and match together instruments to play along with you, scaling their contribution with the intensity at which you play, so that you can experiment around a bit with different scales and musical styles.

The thing that makes Rocksmith the most recommendable serious game ever to me is its difficulty adjustment algorithm, which (again) is based on what was used in the original Rocksmith, but has certainly been refined a bit. The algorithm is most noticable when learning songs, as it dynamically scales the difficulty up or down depending on how well you are doing, providing and maintaining a reasonably appropriate difficulty setting for you to play at.

The game also goes further than only scaling difficulty, but even tries to identify what you struggle with and provides some options to help you get there. In addition, Rocksmith also proposes rehearsal goals for you on the songs you intend to play, in order for you to overcome difficult sections or generally just to push you towards more accuracy while playing. Which, in contrast to the original Rocksmith's way, is much more focused on the learning progress and less on the "score more points to progress" aspect that was more predominant in the predecessor.

Last but not least I should also mention that this game supports (local) 2-player multiplayer, so you can jam with a friend or play the different tracks of a song together. The only downside to this is that it's limited to two players, while most songs consist of three tracks (lead, rhythm, bass) and could thus be played by three people conveniently.

So, in my humble opinion, Rocksmith 2014 is an ingenious game, that really shows how educational serious games need to be made. I can of course not recommend it to everyone, as certainly not everybody is interested in learning to play the guitar, but for all who are (or already know how to and want to have a good tool for practicing and learning a few more songs), Rocksmith 2014 is THE premier choice.