It is loads of fun - you can sing along with the songs or just watch the action. We all loved it....in fact on our recent 10 day trip we saw it 4 times! DH was a hoot - the first time he just went to humor DD and I - then (much to his surprise) he loved it and the rest is history. On our last partial day we went into DHS did 3 rounds of TSM, 2 rounds of Star Tours and a Frozen Sing along and then we hit the road.
We saw it once with a FP and 3 times without. For us we had better seats via Standby than we did via FP - although I need to note for all of the showings we arrived about 10 minutes before show time (so we never showed up far in advance)