No Vim or Emacs style brilliantness, no BBEdit style tons of features and mature engine, no IntelliJ like, er, intelligence, no ST2 comprehensiveness, etc etc.
Plus, the Textmate 1.x text engine was probably a mess too -- I remember the very first versions being laggy (and that's coming from someone who doesn't find even Eclipse laggy). That he couldn't easily fix the one-character-undo is another pointer to that (and, for all I've seen, the 2.x engine is not that better).
It's main saving grace was the many extensions it had, and looking half-decent and native on OS X. Basically, it caught on because it appeared on the right time, and appealed to OS X users like web programmers etc, that wasn't old-time unix buffs, and wanted something native looking without forking for BBEdit (which itself was/is Carbon based and with a custom text display widget).
I don't think Textmate deserved all that success --it should have happened to a better editor.