This is a nice starting island. But some of composers will be harder to guess. (JS Bach, Beethoven, Chopin, Debussy, Glass, Mozart, Pérotin, Rachmaninov, Tchaikovsky, Vivaldi, Wagner...)

Wagner - opera with long instrumental parts, serious, masculine, mighty, tragic. Mahler is much more experimental, polyphonic and mixing different styles, including folklore. Mahler also has many slow moving parts like Wagner. (Mahler, Wagner)

Very simple comparison of two most known classical and late romantic composers. Mozart sounds even (often funny and airy). Wagner - broad and dramatic. (Mozart, Wagner)

More difficult island with two Late Romantic composers both having primarily orchestra and vocal tracks in the game. Bruckner has orchestras and masses and often is more dissonant. While Wagner is more broad, transparent and has mainly operas. (Bruckner, Wagner)