Bruckner sounds closer to Beethoven (repetitive, simple melodic) and Wagner (large orchestral forces including Wagner tubas, progressive harmonic palette, atmospheric, sense of quasi-religious drama), alghough having dissonances too.

Glazunov sounds more sweeping, wide, russian melodic, sometimes dancing, sometimes dark and slow.

Only Bruckner has vocal.

Only Glazunov has violin concerto. (Bruckner, Glazunov)

Bruckner sounds more sweeping melodic, predictable.

Sibelius sounds more unpredictable (melody suddenly breaks or new one begins), dissonant, dark, atmospheric, unearthly, polyphonic, dissonant. Often Sibelius has repetitive back melodies.

Only Bruckner has mass in latin.

Only Sibelius has piano, violin concerto. (Bruckner, Sibelius)

Bruckner sounds more sweeping, serious, powerfull, tutti.

Ives sounds either contemporary and dissonant; or uses USA folk melodies.

Only Ives has piano, organ, string quartet. (Bruckner, Ives)

Bruckner sounds more serious, dissonant, polyphonic, complex, symphonic. Elgar - energetic, expressive, lyric. On this island you will compare Bruckner mass to Elgar songs with orchestra and piano (Sea pictures). March and cello concerto go to Elgar. Elgar also has very atmospheric elegy. (Bruckner, Elgar)

Piano is Bruch. Bruch was born 14 years after Bruckner, but Bruch is romantic solo strings, while Bruckner is post-romantic, complex, serious, polyphonic. Bruckner romantic parts are more often for solo woodwinds. Bruckner also has close to romantic solo string sounds in his mass and some symphonies, so listen longer to string pieces. Bruckner uses harp only in Symphony 8 with string pizzicato and without those long arpeggios like Bruch. (Bruch, Bruckner)

Piano pieces go to Rimsky-Korsakov immediately. Rimsky-Korsakov is more russian folklore, whole tone, orientalism. Watch out for some dissonant and broad sections in Rimsky-Korsakov Le Coq, which can unexpectedly sound closer to Bruckner. Bruckner is generally more slow, wide, serious and dramatic. (Bruckner, Rimsky-Korsakov)

Piano and dances go to Mussorgsky at once. Mussorgsky is generally more simple melodic and rhythmic. Some of more difficult pieces may be Night on Bald Mountain, Sorochinski Fair (Introduction), which are slower and wider, but still contain simple melodies and repetitions. (Bruckner, Mussorgsky)

You will need to skip all those piano, violin concerto and chamber tracks, because they go directly to Brahms in the game. Next simple choice for Brahms will be Hungarian Dances, which sound simple-melodic, rhythmic and light. Compared to Bruckner, Brahms sounds more simple, repetitive, dense and tempo-static like Beethoven. While Bruckner sounds complex, dissonant, wide and slow. Comparing Brahms Requiem to Bruckner mass can be difficult. Brahms Requiem sounds more popular in german and Bruckner mass sounds more religious in latin. (Brahms, Bruckner)

Although these composers were born in the same year, belong to the same period and have mainly orchestral music in database, this island is not difficult at all. Smetana sounds fast, jumpy and dancy. One Smetana piece that is different - Ma vlast, is national melodic, rhythmic, repetitive and linear moving. One important difference from Bruckner will be constant tempo of this movement. Do not answer too fast - Smetana can have a short slow section for you to hesitate. (Bruckner, Smetana)

Should be no problem to guess mass (Bruckner), piano, songs, chamber and dances (Grieg). You might have more difficult time guessing symphonic works: Bruckner sounds to me more serious, slow, wide and dark in this game. (Bruckner, Grieg)

Aside from piano and opera, which go immediately to Rachmaninov, this island seems to me very tough to play on. Symphonic styles of both composers are very close. I think, Bruckner sounds a bit more atonal or dissonating, while Rachmaninov tends to use more lyrical and simple melodies. (Bruckner, Rachmaninov)

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

Bruckner - more serious, slow, polyphonic and dark. Ravel - piano, transparent, rhythmic. (Bruckner, Ravel)

Bartók is piano, atonal, chaos, folklore. Bruckner is more romantic and traditionally symphonic in this game. Also, do not forget Bruckner's mass. (Bartók, Bruckner)

This seems very difficult to me. Apart from Saint-Saëns having opera and piano and Bruckner having mass, it is more difficult to guess the author of orchestral pieces. Saint-Saëns seems to be more light and Bruckner more heavy and complex/polyphonic. I would be glad to see better guidelines in comments here. (Bruckner, Saint-Saëns)

Dvorák sounds dancing and light, simple popular melodies most of the time. Bruckner is either more serious and tutti, or more complex, dissonant and polyphonic. (Bruckner, Dvorák)

I find this island to be one of the most difficult island with Bruckner. Composers are very close. R Strauss has operas, Bruckner has masses in the game. Orchestral pieces sound close to me. How could you distinguish them? (Bruckner, R Strauss)

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)

Prokofiev sounds more contemporary than Bruckner, more rhythmic. (Bruckner, Prokofiev)

Comparing Bruckner and Mendelssohn, I continue to be surprised by the tenderness of some melodies of Bruckner. I think of his music as being radical, but it is not always so. (Bruckner, Mendelssohn)

Debussy seems more airy, Bruckner is more grand like Wagner, but also has dissonances and light melodies. (Bruckner, Debussy)