He's definitely one of the deeper and more interesting characters in the series. While there are a lot of interesting characters, not many of them play that far outside their roles (Data always being curious and naive, Troi always being sensitive (except for the command test episode) Vulcans always being Vulcans (except for 4th season T'pol) Geordi always being blind, etc)
Garak is a great character not so much because you want to emulate him (though I really kind of do sometimes) but because you want to understand him. Discovering what makes him tick is what makes him inspiring. You don't get that inspiration with 'flatter' characters like say... Dr. Crusher, or Malcom or Riker.
The captains get some playtime with this, but to me they always come out as fairly consistent characters by the end, not really changing much from their experiences (Picard dealing with being borg, dealing with 4 lights equaling 5. Janeway dealing with what side of her bed she rolls out of and whether or not she's going to blow up a civilization today to get home a little faster, or save them instead of getting home immediately. Sisko with being a wartime captain and being space Jesus. Archer with doing nothing for the first two seasons, then fighting terrorism in the last two.) Though out of all of them, I'd argue Picard may have made the biggest shift, going from a naive, grumpy man in dealing with Q in the beginning to becoming a not-so-naive, slightly less grumpy, more optimistic old man by the end. Again, the redshift isn't huge, but it is measurable.
On the whole though, I feel like despite TNG's mantra of trying to be classic Star Trek with a modern twist by developing stories introspective of modern society, DS9 was actually the most introspective so far. Probably has to do with the war.
