In some ways it's kind of ironic, but probably the thing that jumps out the most in such a comparison is that VS and Eclipse both have a lot more eye candy. They are more visually appealing programs, at least in my opinion. XCode is a little more stripped down, and not just in the eye candy department.
A popular feature in IDEs is code completion, popularized by VS's IntelliSense. I don't know if VS was the first IDE to have this, I just know it made it popular. I actually think Eclipse does this better than VS these days. XCode has this feature, too, but it is turned off by default. There is something appealing about that to me. Code completion can make developers lazy, and some would argue that it decreases your programming skill. It's hard to argue that it doesn't make you more productive, though. XCode should make better use of it and turn it on by default.
XCode is very good for running and debugging. I was impressed that it gave me an error code in a program that didn't clean itself up properly. Of course that error message was very cryptic, and was just a warning. Only after I fixed the problem did I realize that the weird warning was because I had left some garbage on the heap in the program.
All of this made me think, I wonder if there is an Eclipse plugin that's designed to enable Mac development? The answer is no, and for a good reason. Eclipse is a little clunky on the Mac because SWT is implemented in Carbon, not Cocoa. Most of those super-slick Mac apps out there use Cocoa. SWT binds the native UI elements on whatever system it is running on, so it could use Cocoa or Carbon on the Mac. The SWT developers chose Carbon. They had some very good reasons for doing so, but the end result is Eclipse is a little clunky. It's hard to convince somebody who wants to build a slick looking Cocoa app to use Eclipse.
Anyways, XCode holds up pretty good, though it definitely seems like a notch below VS and Eclipse. Let's face it, appealing to developers has never been Apple's strong suit. Dashcode is kind of promising, though widget development is definitely a niche at this point.