No way they should return to Beast of Chaos, it was not even an army book it was an addition to Hordes of Chaos. No Marks! I just can't picture Tzeentch/Slaaneshi Bestigors and Minotaurs
Also I like the new fluff, all the dung-smearing and pure destruction gives them a clear personality. I love the story behind their hatred for Mankind. They should however delve more deeply in the Secret War with the Wood Elves, have an extensive love-hate partnership with the Chaos Warriors (not Daemons) and have some fluff about their quarrels with other denizens of the forrest (Forrest Goblins, Vampire Counts, etc)
Rule wise I agree with most what has been said here (cheaper rares, etc) but i still miss some wakier stuff in that army like what the Vampire Counts received.
Almost forgot, a unit of supa-Tuskgors (Razorgors) feels kinda lazy to me, there is more interesting stuff to make then that imo.