Noone liked Apple's round hockey mouse shipped with the original iMac. It was just awful. Too little. Too round. Bad designer, no cookie.
Some people don't like the newer (from 2000) "pill mouse" either.
I am not sure what's not to like about it. Most people rant about only having one button. Sure, when I used LinuxPPC I sorta missed a second button. In OS 9 I didn't at all and in OS X I honestly don't either. I think Viridiana has something against the size, which is my only possible complaint. It could be a bit taller for my hand. I have to ask her what it is she doesn't like.
So what do I like about it? Well, the things you become aware of when parts of your body becomes oversensitive (to put a semi-positive spin on it).
I love that there's no button. For my sore, tired arm and hand it's a total blessing to to put a bit more weight down instead of doing some awkward movement of one finger to a particular place to activate. Trust me, when your body throws in the white towel you'll know what I mean.
The adjustable click-tension will let you to make it work optimally for you. I usually have mine set to the ligh setting. If you have a heavier hand you just change it to require more pressure to click. Viola!
And then it looks neat, which is never bad.
All that being said it seems like Apple are coming out with a new keyboard and mouse. It's hard to judge the mouse without trying it (no major redesign except for apparent loss of the click tension thing (suck!)). But the keyboard, oh dear, the keyboard! From the pictures it looks like it's getting a heavy tilt built in.
That's #$%#$% backwards you idiots. The natural position for the hands is the other way if anything! No, years of keyboard design with optional tilt from the back has not changed it; quite the opposite.