What I liked: well, I didn't actually like anything beside the ease of modifying/adding keybindings.
Some of what I didn't like:
* The whole UI felt wrong from alpha to omega and overly gimmicky: the whole thing relied too much on the mouse and the things that relied completely on the mouse like the options in the search panel were poorly sized/designed. The many roundrects and shades and gradients created a mess that left a very bad impression.
* The underlying engine is very poorly used by ST: just activating vintage mode is enough to tap a lot deeper than the default UI lets you. The engine is great but it only shines when you try to use it as another app. That's weird.
Using Vim is a spoiler, I guess.
I can't reasonably tell you to not make the switch. I have no idea what knowledge you have of Vim but I can say that I find Vim not only extremelly more powerful than ST but also a lot better designed on almost all fronts.
Once the beauty of subsitutions, :global, ranges, Ex commands, text-objects and motions is ingrained in your brain, using ST2 may feel like using (a pretty) TextEdit. Hell, even folding is nicer in Vim.
In the last year, I had the impression that a bunch of people blogged about their decision to switch to ST2 from Vim. Each time, I felt that the blogger didn't use much of Vim to begin with so switching may have made some kind of sense. If you are reasonnably advanced, I don't think there's any reason to switch.
But the find panel is the sole reason I cannot use ST2. Every time I bring it up I can't remember what button does what. And then I get stuck in the panel and have to click to get rid of it. Or hit escape.
But if I hit escape before hitting enter it assumes I didn't want to search after all and scrolls the viewport to somewhere random. Even though the term I wanted to search for is clearly highlighted on the screen.
It's a very very frustrating experience and even my co-worker who uses ST2 every day for the past year or two still gets tripped up by the find panel.
If I had a way to import the TextMate 2 find dialog into ST2 /3 I would buy a license.
There is Vintage mode, but IMO it doesn't work very well. The differences are small but numerous, and it's very annoying when the behaviour doesn't match Vim's. Others have rightly pointed out that many advanced features are missing, but I'm not talking about those - I'm talking about your bread and butter navigation/editing commands.
To make matters worse, while there is the occasional pull request, official development of Vintage mode seems to be at a complete halt.
I purchased Sublime and really, really tried switching to it (I think I gave it about six months), but I had to switch back.
I really liked Sublime but VIM like a good pair of Levis' 501 never goes out of style.
I like textmates uniform OSX style and VIMs uniform terminal style, using the "Tomorrow" theme on both [1].
Although I'm also a part designer so the aesthetics matter to me as much as functionality. If you're measuring functionality I can't imagine sublimes better than VIM.
The advantage of sublime is that it works well out of the box and with package control it is very easy to install any package you may need.
If you decide to give it a try, try sublime 2 with package control (I believe the trial is still free for sublime 2).
Sadly I can't run ST2 on our work machines as the RHEL version we use has a libc (glibc?) that is too old. I'm unable to host my own libc due to a binary format change that is incompatible with the system dynamic loader.
It's better than IDEAVim, but certainly ViEmu and jVi are better. Maybe even Vrapper and XVim beat it too.