Conversation so far:
what is the origin of neutral milk hotel?
Jeff Mangum, along with high-school friends Will Cullen Hart and Bill Doss, formed The Olivia Tremor Control.
what was their first  release?
Mangum appearing on their first release, the California Demise 7".
did they have a different name when they started?
Neutral Milk Hotel moniker, Mangum recorded a few cassettes under the name Milk.
what were some of these casettes called?
1991's Invent Yourself a Shortcake, 1992's Beauty (not to be confused with the earlier cassette), and 1993's Hype City Soundtrack.
did they produce any hits?
CANNOTANSWER.
what other songs were on the cassettes?
Another track, "Digestion Machine".

Question: what genre of music did they play?
Self-contained rewrite: What genre of music did Neutral Milk Hotel play?