- The "depth of catalog" is actually incorrect -- Spotify has far far more songs than Napster did (you can see in that screenshot even, most logins/servers hit less than 1m songs totally available, and of course those are just total indexed, in reality almost 50% of downloads would not be available.) Yes, you could find niche stuff on Napster-- as a musician in 1999 I would make sure all my stuff was available, pre-release, demos, etc. But we have Soundcloud for that now, so...
- The discovery on Napster was non-existent. You could browse through a users' collection, the same way you can browse through playlists today. But the only entry into anything was a search box that only looked at ID3v1 data and filenames. There's been amazing leaps and bounds in discovery since then, and it's very clear by the #s that it's what people wanted -- a guided (radio, playlist) experience over a wild west single song retrieval thing.
- Napster was stupid bad at search. There obviously was no catalog resolution and the quality of the results was abysmal. I am pretty sure it was a substring match, for one, and then there was the bad metadata, fake songs, later on a huge spam / "SEO" problem.
- Not going to get into speed, because it wasn't Napster's fault, but even back then it was far easier to get music elsewhere other than Napster if possible. Ratio FTP sites, hotline, and of course bubblecruft startups building customer bases by selling new CDs for $4. It was very clear at the time even that the distributed nature of Napster was a liability, not a promise, as all the single-server solutions were far more convenient and reliable. But this was not their fault and of course their success inspired everything after it.