The Waldstein is a titan of the keyboard repertoire, pushing the piano to its physical limits during the early 19th century. Its brilliant, orchestral scale and technical demands set a new standard for virtuoso sonata writing.
Achieving evenness in the rapid, alternating-hand passage work and the daunting octave glissandos is the primary challenge.
Comparable difficulty and character — good candidates for what to learn next.
Piano Sonata No. 21 'Waldstein' (Op. 53) is rated Henle level 8 of 9 — concert repertoire, roughly diploma level.
You should be comfortable at Henle level 8 — meaning you can already play level 7–8 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 Piano Sonata No. 21 'Waldstein' (Op. 53) lasts about 25 minutes.
Piano Sonata No. 21 'Waldstein' (Op. 53) 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 Rondo a capriccio in G major by Ludwig van Beethoven, 32 Variations in C minor by Ludwig van Beethoven, 12 Variations on 'Se vuol ballare' by Ludwig van Beethoven — see the full similar-pieces list on this page.