Quite simply, I keep looking at it and it doesn't endear itself to me over time. Even GMail's web interface is better, and Outlook definitely is. I know that most people probably just use a client (whether it's Apple's own or a third party), but sometimes I just need to access it from the web and it's just plain awful. Some of it is just general UI badness, and some of it is ... well, an example is how the fonts look on IE 11. They're not just poorly sized, but it looks like a pen that's starting to fade. I just looks awful. And that's not even mentioning the big functionality problem I have with it!