I have had my 100mm macro for a bit now and can give a little review of what I have found out. The lens is super sharp!! As far as clarity, this lens definitely battles my 17-40L. The lens a little hefty for a prime but nothing that can't be dealt with. Typically, manual focus is the way to shoot with this lens. AF can hunt a bit. But, the quality is by far worth the hunting. In my opinion, the only thing thats not "L" about this lens is the infamous red ring. The true macro is fun to play with. Excellent for portrait as well, however its a little long on the crop (1.6x) camera. Also, sometimes I wish it was a little faster than 2.8, but what can you do?
Overall, the pros crush the cons. Buy this lens!!