Grieg sounds more simple, repetitive, transparent (solo piano). Often (piano concerto) energetic and excessive.

Only Grieg has string orchestra.

Only Tchaikovsky has piano+violin+cello. (Grieg, Tchaikovsky)

Brahms sounds more repetitive, uniform, classical. Some piano pieces sound surprisingly cosmic, abstract.

Tchaikovsky sounds more sweeping, broad, russian, post-romantic.

Only Brahms has piano+clarinet+cello, piano quintet, clarinet quintet, violin sonata.

Only Tchaikovsky has piano+violin+cello. (Brahms, Tchaikovsky)

Smetana sounds repetitive, simple and often very energetic.

Tchaikovsky sounds different - more sweeping or more dancing.

Only Tchaikovsky has piano, vocal.

This island seems difficult to me and I would be glad if you add valuable comments here! (Smetana, Tchaikovsky)

This is a simple island, but some pieces can be harder to guess.

J Strauss II sounds extremely straightforward, consonant, monophonic and simple-melodic (not always sounds like waltz).

Tchaikovsky, even in his simple dancing pieces, sounds more complex and polyphonic.

Only Tchaikovsky has piano, instrument concertos. (J Strauss II, Tchaikovsky)

Berlioz sounds more classical, pathos, bravura, eccentric, eccessive orchestrated.

Tchaikovsky sounds more national russian singing melody, dance, sweeping.

Only Tchaikovsky has piano, russian vocal.

Only Berlioz has french vocal. (Berlioz, Tchaikovsky)

Tchaikovsky sounds more russian melodic, sweeping, energetic, dancing.

Fauré sounds more classical, serious, straight rhythm, predictable.

Only Tchaikovsky has piano+violin+cello, russian vocal.

Only Fauré has piano with violin, piano with cello, french vocal. (Fauré, Tchaikovsky)

Tchaikovsky sounds more simple russian melodic, dance, light.

Sibelius sounds more chaotic, polyphonic, atmospheric.

Sibelius violin concerts sound more energetic.

Only Tchaikovsky has piano in this game. Sibelius has only one female piano song. (Sibelius, Tchaikovsky)

This is a comparison of romantic Mendelssohn and late romantic Tchaikovsky.

Mendelssohn sounds conservative, cold, closer to classical.

Tchaikovsky sounds more sweeping, dance, folklore, song-like.

Beware of Mendelssohn Hebrides, which can sound more romantic. Mendelssohn Songs without words sound like piano playing a vocal part. (Mendelssohn, Tchaikovsky)

This is a simple comparison of romantic Schubert to late romantic Tchaikovsky.

Schubert sounds more classical, repetitive, simple harmonic, simple structure, closer to Mozart. Some Schubert piano pieces can be slow, but they will still be simple harmonic.

Tchaikovsky sounds more sweeping, dance, folklore, song-like. (Schubert, Tchaikovsky)

Sousa sounds march, simple.

Tchaikovsky sounds more serious.

Sousa has only music for wind band. (Sousa, Tchaikovsky)

Compare two most known late romantic russian composers.

Tchaikovsky sounds more dance, light, percussive.

Rachmaninov sounds more serious, brutal, sweeping.

Only Tchaikovsky has piano+violin+cello in this game.

Only Rachmaninov has religious chorus. (Rachmaninov, Tchaikovsky)

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...)

Tricky bits on this island are Organ compositions of Pérotin (that can sound JS Bach if you don't listen long enough) and piano Tchaikovsky, that can also in haste be messed up with Glass. (JS Bach, Glass, Pérotin, Tchaikovsky)

This is an interesting island of two russian composers, known for their sweet energetic dancing music.

Tchaikovsky is generally more sweet and broad.

Dunayevsky is more simple, energetic and popular.

Only Tchaikovsky has vocal pieces in this game. (Tchaikovsky, Dunayevsky)

Vivaldi and Bach are unexpectedly confusing on vocal pieces. The rest three can be simply recognized within 3 sec. (JS Bach, Glass, Perotin, Tchaikovsky, Vivaldi)

Gershwin should be no problem to guess. While two others are both russian and both can sound wide and melodic at times. Lighter pieces with pizzicato and melodic percussion are more common for Tchaikovsky, while Shostakovich usually sounds more serious and depressive. (Gershwin, Shostakovich, Tchaikovsky)

Bruckner has symphonies and mass in the game. Slow, serious, polyphonic. Tchaikovsky - piano, opera, ballet. Russian, melodic, repetitive, expressive, energy. (Bruckner, Tchaikovsky)

Two symphonic late-romantic composers. Tchaikovsky is dancy and russian. Mahler mixes everything and often at the same time, but generally sounds more slow or yearning than Tchaikovsky. Yet, Mahler also has folklore melodies. (Mahler, Tchaikovsky)

Not very balanced island. Pérotin is renaissance. Tchaikovsky is orchestral and dance. Glass is contemporary and minimalistic. Bach and Vivaldi are baroque. Everything is easy here except for choosing between Bach and Vivaldi. You can also see my comments on JS Bach/Vivaldi island. (JS Bach, Glass, Perotin, Tchaikovsky, Vivaldi)

Don't be afraid that this island has 4 composers. They are all very different. Pérotin is renaissance. Bach is baroque. Tchaikovsky is orchestral and dance. Glass is contemporary and minimalistic. (JS Bach, Glass, Pérotin, Tchaikovsky)

Comparing two of the most known composers of two very different periods: Baroque and Late Romantic. (JS Bach, Tchaikovsky)