Even nerfed M'uru is hard -- he's the first really challenging boss in Sunwell (twins was hard, except the 'reverse', shadow-first strat makes it far easier.)
Expect to spend several weeks on him since your sides will need to learn how to control aggro/keep threat high (this is the biggest challenge), your sent/void tanks will have to learn how to coordinate -- and then phase 2 is a whole set of learning in and of itself. Your win/lose is definitely dependent on your two side groups, and most of all on those two tanks.
It's still a challenging encounter even with the nerf.
So far, my guild has had about 150 wipes and today, we finally managed a perfect transition to phase 2, and got entropius down to 15%. We expect him to go down on sunday, barring some unforeseen afk's or fuckups
We're at the end of week 4 now, and we got entropius to consistently to phase 2 and had increasingly good attempts, finishing the night at 4%. Planning on finishing him tonight. /pray