Being a lover of both classical and rock music, I occasionally dig rock adaptations of classical music if they are really well done. The pretty much undisputed master at this game was Keith Emerson, the classically-trained keyboard virtuoso who was the center of Emerson, Lake and Palmer.
What made Emerson so unique was not his extensive Bach quotes (many other progressive and hard rock musicians indulged in those, albeit to lesser degrees), but his predilection for the darker sounds of 20th-Century classical music. In some cases, his arrangements are almost more effective than the originals in creating the moods they sought to evoke.
Below is Exhibit One, “The Barbarian”, which is an arrangement of/fantasy on “Allegro Barbaro” by Bela Bartok. The actual piece starts about 38 seconds inside the video. A middle section on piano — pretty much the original, highly percussive, piano piece, but played with Emersonian drive and panache — is sandwiched between heavy rock sections in which Emerson turns themes from the original into scorching heavy rock riffs played with his unique overdriven-yet-clear Hammond organ sound. Carl Palmer’s pounding, yet creative drums and Greg Lake’s nontraditional use of the bass guitar add their contribution to create an atmosphere where you can just visualize a real ‘barbarian’ going berserk.
Below is one of Emerson’s final concert recordings before carpal tunnel syndrome — every classical pianist’s worst nightmare — took him out of commission almost permanently. This is a rock arrangement of the main theme from the ballet ‘Romeo and Juliet’ by Sergei Prokofiev: the biting synthesizer sounds work surprisingly well with Prokofiev. This was a bootleg live recording, so I apologize for the sound quality: here is an excellent cover version with better sound.