Cowell's 'Anger Dance' utilizes percussive tone clusters and driving rhythms to create a visceral, aggressive sonic landscape. It is a quintessential example of early 20th-century experimental American piano music.
Focus on extreme accuracy in striking the clusters to avoid unwanted muddy textures.
Comparable difficulty and character — good candidates for what to learn next.
Anger Dance is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Anger Dance lasts about 2 minutes.
Anger Dance is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Boléro by Maurice Ravel, Étude in C minor, No. 12 by Frédéric Chopin, Prelude in G minor, No. 5 by Sergei Rachmaninoff — see the full similar-pieces list on this page.