The user reports I've seen have been favorable. The 100/2.8 was always a very sharp lens, so you couldn't expect too much improvement there (though the new lens does have an "L" designation). The
Canon EF 100/2.8L IS Macro USM has hybrid Image stabilization which works on multiples axes and makes hand held macro work
much easier. I hope to get one to test in the future, but I'd say you won't go far wrong if you buy one before you see a test!