This piece utilizes a sparse, quasi-atonal language typical of Blacher's later style. Its distinctive feature is the use of variable meters within a strict contrapuntal framework.
At Henle 5 this is a late-intermediate piece — technically substantial, with musical demands to match. The main demands: independent voices that must each sing on their own line; precise articulation — the difference between crisp and blurred is the piece; and chord voicing — bringing out one note inside a handful of others.
Focus on the separation of voices, as the independence of the two lines is the primary technical hurdle.
Comparable difficulty and character — good candidates for what to learn next.
A level or two down with the same spirit — ideal if this piece is still out of reach.
Where this piece's skills lead: slightly harder works making similar technical demands.
Dialog is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 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 Dialog lasts about 4 minutes.
Dialog 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 Ciacona in D minor, P.41 by Johann Pachelbel, Ballade en mode phrygien by Jehan Alain, 12 Variationen über ein eigenes Thema by Alban Berg — see the full similar-pieces list on this page.