Here are three things I love about it:
TabsLike Firefox with web pages, Komodo uses tabs to present multiple documents in a single window. Tabs blows away every previous MDI approach for usability, and I wince whenever I have to use an application (TextWrangler, emacs) that presents multiple documents in any other way.
Indentation Adjustment This may sound trivial, but Komodo has the easiest keyboard shortcut for adjusting indentation of any editor I've ever used. Just select the lines (or portions thereof) you want to indent and press the Tab key. To unindent, press Shift-Tab.
Komodo will indent using tab characters or spaces per your settings (which you can set for individual files) or by sniffing out the indentation strategy already in use in the file.
Fully-Configurable Key Bindings and Syntax HighlightingI almost never tweak these settings, but it made a big difference to be able to do so when I first started using the application.
In Komodo, every keyboard shortcut is configurable, which I used to change "Find Next" from F3 to Ctrl-G and "Go to Line" from Ctrl-G to Ctrl-L to match what I was used to from previous editors.
Syntax highlighting is also customizable--including font family, size, color, and background color--down to individual language elements, so you can give JS variables, HTML attributes, and Python comments their own individual styles.
Komodo also provides an Emacs key binding scheme and a Vi compatibility mode, if that's your thing. And it includes several built-in highlighting schemes, so you don't have to design your own from scratch (I started with "Dark" and made a few tweaks).
Everything ElseThere are tons of other things to love, of course, like integrated debugging for half a dozen scripting languages, remote file access via S/FTP or SCP, code completion, background syntax checking, integrated source control for CVS, SVN, and Perforce, and so on.
And then there are the features I haven't learned to love yet, because they're new in version 4.0, but which I expect to come to rely upon in the future, like support for Firefox-style extensions.
Did I mention that it's cross-platform (Windows, Mac, and Linux)? If you're looking for a great text editor/IDE, check it out.