Every Mac OS release sucks depending on who you ask. Some people think everything after Panther has been utterly useless. Some even think OS X is not much better than Classic! (seriously). Point is, people aren't big fans of changes...at least initially. I'm no exception.
People hated Tiger because they felt the UI was uglier (capsulated blue buttons, loss of pinstripes/brushed metal), Spotlight was lame, Finder unusable, and overall, Tiger was slower, buggier, more of a resource hog and it broke this and that blah blah blah...
They thought it was a step down from Panther which was the king of all OS X releases.
People also hated Leopard when it debuted; They mocked the 3D dock and its loss of functionality (e.g. no list view, stacks), as well as the transparent menubar (people even laughed at the slide when Steve unveiled it). Others thought the UI changes were dire, full of fluff and hampered usability/functionality (grey folders and glassy buttons). Also it was slower, buggier, more of a resource hog and it broke this and that blah blah blah...
Compared to Tiger, the king of all OS X releases, Leopard was a joke.
In Snow Leopard people thought its Expose implementation sucked and was a step down from Leopard/Tiger (now people are crying for it back in Lion), they also bemoaned the fact that the UI changes hadn't been corrected, and that there were no new features and Finder was still broken so there was no point upgrading. Also the classic; 'buggier, slower, it broke this and that' blah blah blah. Compared to Leopard, the king of all OS X releases, Snow Leopard was nothing more than a service pack release.
Every version of Mac OS released 'sucks' in one way or another. Yet people somehow manage to survive them...10.7/Lion will be no exception.