The fact that the file list correlated to the contents of a directory was a huge deal. XCode and other editors require "projects" to be assembled. TextMate could also ignore certain paths if configured correctly, cleaning up projects considerably.
I used SubEthaEdit prior to TextMate and was quite happy, but it lacked multi-file editing and tabs.
However, those 4 features were what moved me over to TM - I was more than willing to plunk down my $50 for these features that no other editor (at the time) had