This early nocturne possesses a profound, brooding depth expressed through its chromatic harmonies and long-breathed phrases. It is distinct for its shift from a mournful minor section to a surprisingly bright, hopeful middle episode.
The player must master long, sustained phrasing that requires careful weight distribution for a truly 'cantabile' tone.
Comparable difficulty and character — good candidates for what to learn next.
Nocturne in B-flat minor, No. 1 is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 9.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 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 Nocturne in B-flat minor, No. 1 lasts about 5 minutes.
Nocturne in B-flat minor, No. 1 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 Prelude in D-flat major, No. 15 by Frédéric Chopin, Nocturne in C minor, No. 1 by Frédéric Chopin, Nocturne in C-sharp minor by Frédéric Chopin — see the full similar-pieces list on this page.