I'm sure it's fast, but also consumes a ridiculous amount of memory. Tried loading a smallish dataset into neo4j that runs on a 100mb ram postgres server just fine. Neo4j wanted gigabytes of memory.
It was also alarmingly weak on data-integrity protection features, like constraints, locking, and data-types, at the time. IDK, maybe they've fixed that. Then, it was IMO wholly unsuited to hosting any data set that you couldn't stand to have completely destroyed every so often (so, a very particular kind of caching, which IIRC is exactly what one of their marketing department's favorite names to trot out, Ebay, used it for then).
[EDIT] I would, however, agree with nisa's post elsewhere in the thread, that the Cypher query language is excellent.