On the subject of the DOM, I've actually had a few instances where IE wouldn't redraw. That is, I would alter an element and it wouldn't appear to be affected on IE. I ended up resizing the element to force a redraw. Bugs like this (especially when you get into CSS support) FireFox (and Opera) much more appealing to web developers. Because when it comes to supporting and implementing web technologies, Trident lags behind all the other rendering engines.
Even from a User's perspective, there are very little positives. I'd say that with IE you have one advantage: You know 99.99% of pages will work with it. That's all I'll give it. You may say it's faster, it's slower whatever. Firefox actually turns out to be slower than IE (Not that you may notice it on newer computers, and Gecko tends to start drawing the page before Trident will. What this means is that Firefox will start to show the page as it comes in and IE tends to wait to receive a large chunk of the page before it starts showing it) and Firefox also uses more memory than IE. But, Opera, on the other hand, beats out both hands down. Faster, lighter, and very standards compliant.
IE isn't a beast because it does more. It doesn't support more, actually, all the competition supports more. IE is a beast because IE 6 is at this point about 4 and a half years old, while all the other competition had releases in the second half of 2005. IE development stopped for a while. The core rendering engine is even older code that hasn't had any serious development since Version 5, which was over 7 years ago. Since IE has to keep all these old hacks in their Legacy rendering to keep a large chunk of websites working, while also trying to support the new standards, on code that hasn't had any serious rewriting in several years - you tend to get an underperforming browser.
