Why Sublime Text 2?
Speed. It’s got the responsiveness of Vim/Emacs but in a full GUI environment. It doesn’t freeze/beachball. No need to install a special plugin just to have a workable “Find In Project” solution.
Polish. Some examples: Quit with one keystroke and windows and unsaved buffers are retained when you restart. Searching for files by name includes fuzzy matching and directory names. Whitespace is trimmed and newlines are added at the end of files. Configuration changes are applied instantly.
Split screen. I never felt like I missed this that much with TextMate, but I really appreciate it now. It’s ideal for having a class and unit test side-by-side on a 27-inch monitor.
Extensibility. The Python API is great for easily building your own extensions. There’s lots of example code in the wild to learn from. (More about this later.) ST2 support TextMate snippets and themes out-of-the-box.
Great for pair programming. TextMate people feel right at home. Vim users can use Vintage mode. When pairing with Vim users, they use command mode when they are driving. I just switch out of command mode and everything “just works”. (It also works on Linux, if that’s your thing.)
Updates. This is mainly just a knock on TextMate, but it’s comforting to see new dev builds pushed every couple weeks. The author also seems to be quite responsive in the user community. A build already shipped with support for retina displays, which I believe is scheduled for a TextMate release in 2014.