The main differences that I've seen so far are in loot quality and distribution (items all have RNG stats/names, and drop randomly from mobs). Also, the skills in WH:O are much more in-depth and complex. There's a lot of comboing potential (e.g. if you have X skill active, Y skill has an extra effect and/or does more damage).It's quite disappointing, after watching gameplay videos there is awfully alot of similarities between the gameplay, only difference is the storyline.
You can definitely tell that CH was a major inspiration for WH:O though. I personally don't mind it though.