It's really good! It's seriously up there with the best reverb plugs going around. Cleverly, rather than making it Accel only, there's an Accel version AND an HD version.
I think its best asset is its inteface which easily and graphically allows the ER section to split off from the reverb tail section. You can make really convincing small rooms with very little effort just by messing with the ER section with the reverb tail turned off. Other reverbs might offer the same control of course, but I personally just found it really easy to get into because of the way its laid out - and the quality of the tails is top notch.