Well, a good place to start would be that it works (CSS 2.1, XHTML 1.1, HTML 4.01, WML 2.0, ECMAScript, DOM 2 and SVG 1.1 basic)
A good following point would be that it not only does a lot (not always important, depends what you want), but does it easily (such as fully intergrated search (keywords in addressbar, rather than a seperate box; e.g: "g something" would do a google search on "something"), fastforward, voice and mouse shortcuts, quicklaunch, and trashcan)
Then theres always the fact its as secure as browsers get, faster than FF or IE (trust me, my connection and system are both slow enough to make this noticeable), accessible (voice, zoom, stylesheet changing, toggle gfx and ss)
Lastly, theres the fact that when I'm not viewing the web I like writing the web, and the ability to make changes and reload from catch, the devtools for DOM JS and CSS, shortcut for validation and the fact that it correctly uses media type stylesheets (printing uses print, fullscreen projection, smallscreen mobile, handheld, etc.)
Theres s***loads of other stuff, but they're the main reasons I use it. To me it just seems a lot of browsers just try to cram in features and overlook the basic fact that web browsers are meant to render web pages, and most don't do it as well as they could. The two exceptions I find are Opera and Safari both work beautifully, but of them, I find Opera easily the more efficient to use, and most useful when not just reading a screen.
Likewise, when I'm at TAFE and just want to look at some pages rather than write anything or keep dozens of pages going at once (tab control in Safari is f*****), then Safari is my browser of choice.
EDIT @ Blodo: Likewise, FF can be a real pain sometimes. But then, check
Opera,
IE, and
FF features and look for which doesn't mention CSS support
EDIT AGAIN: So wait, neither of you have other browsers installed?