In fact Grimmjow's release is nothing special. It's like a cool looking outfit with effects similar to the Tensa Zangetsu (increased speed, power, nothing too special).
And well, hate to spoil, but he ends up getting his ass handed to him by Vizard Ichigo. As would obviously happen sooner or later.
Don't get me wrong, Grimmjaw is one of my favourite Bleach characters. It's just that the way Mr. Kubo suddenly made him into a 'piece o' crap' character by getting Noitora treat him like garbage (he makes a freaking "surprise!!" look on his face, dammit! Ichigo makes "surprise!!" faces, not Grimmjow!) really sucks. It's awful when a really cool character is treated as a defenseless, disposable plot device.