This is another one that probably doesn’t count as a Rhapsody but it does fit most of the criteria: i.e “Irregular in form and improvisational” so I’ll run with it. This is “Seven Angels” by the band Avantasia (Lead singer Michael Kiske) from their Metal Opera collection. (done up as a Justice League fan video)
I’ve enjoyed this piece for some time. My tastes tend to be pretty eclectic. Everything from chamber quartets to Metal. But one thing I tend to lean towards longer and more complex pieces. It’s always great to hear modern music that starts to lean this way. Regrettably most of them tend to be fairly short feeling very much like musical phrases. Snarky remarks about modern attention spans aside I see no reason why they can’t be more ambitious.
Anyway here I think this is one of the better attempts so far. So enjoy.