The main things that put me off at the time were the the badly-designed menu structure (which it still has), its rather bleak Preferences dialog, and a fascinating amount of obscure key bindings that seemed to go on forever (and make absolutely no sense).
That and an utter lack of Python support at the time was more than enough to offset niceties as its project drawer, decent Unicode support and, above all, its "Filter through" command (which was what I needed most at the time).
I don't code for a living anymore - I code for a hobby, and as such what I need in an editor is something simple, intuitive, and that doesn't get in the way. Oddly enough, I've found either vim or SubEthaEdit to fit that bill, the first due to years of indoctrination and hard-wired reflexes and the second due to its "no frills" approach.
But I've a few years of coding and editors under my belt, and the benefits of niceties such as completion, folding, SCM integration, etc., have been pretty obvious to me since my Brief and Visual C++ days.
So even though I make it a point of being able to do without them or never customizing whatever editor I use to the point where I'm wholly dependent on it, TextMate makes some things pretty easy for me.
For instance, it's a great mini-IDE to develop for Snakelets - the script output and documentation windows are pretty damn useful, and the project drawer and Subversion support (complete with diffs and other niceties) make it easy to keep track of things across my iMac and iBook.
But ironically, Quicksilver's User Interface Plugin is the main reason I find TextMate's UI tolerable right now - precisely because it saves me the time involved in hunting through umpteen menus for what I want.
So TextMate still needs a lot of UI polish, and Melo (who has been trawling the mailing-lists and becoming one with the editor as only a true vim Jedi can) tells me that the next “major” release will focus on the UI (and possibly remote editing, which would be nice) and that the one after that will improve the folding system.
It will be a while yet until it's "perfect" (at least for me, since I'm still somewhat annoyed by what it considers to be Python "folding"), but all things considered, the progress in the meantime (and the new fancy input manager plugin Melo mentions) was enough for me to decide to bite the bullet and become licensee #4944.
And it's all Mac-only.