I spent a great deal of time reading through Warhammer: GROM in detail a few months ago when Kevin first released this expansion. This book is great, if you enjoy reading through GW army books you will also enjoy this one. The fluff, art work, new army lists and overall content are all top notch. It is worth the read.
I said as much before on Da Warpath, but this is a great book. I don't agree with making new rules for Forgeworld models that already have rules (even though they are out of print) but that is a very minor point).
After my summer of playing ET: Nagash scenarios though, I went back and looked for Grom scenarios and discovered that there are none! A bunch of scenarios set before and during the end times and featuring Grom and other legendary Warbosses from across the Warhammer world would be a great addition to this work.