As far as 6 mana Werewolves go, I think I still prefer Tovolar's Huntmaster since the 3 bodies can stabilize the board better. But Hexproof is nice so that your 6 mana investment isn't immediately removed. I could actually see this being better than Carnage Tyrant. As long as you have another creature, it's 8-total power on the first attack compared to 7 power on Carnage Tyrant, and even without flipping, those numbers keep going up each turn. The backside is very good, but my experience so far is that Werewolves need to be evaluated on their front side.
edit: I forgot Carnage Tyrant also can't be countered. Carnage Tyrant still may have the edge on this one because of that.
This is a pretty annoying card with powerful abilities, but it sits between a rock and a hard place between what it wants to do. As a single threat hexproof threat, Carnage Tyrant is generally the better option since it's uncounterable, has trample, and doesn't rely on other creatures to get the full value out of it. As a +1/+1 matters enabler / payoff, it's generally worse than Vorniclex, Monstrous Raider. Tovolar's Huntmaster creating its own threats is more appealing to me than adding +1/+1 counters to other creatures.
Citadel Siege on a green creature! I still play that card and think it's great, so I'm excited about this one.
If you can attack the turn you play this, this has a faster clock than Tovolar's Huntmaster. For example, in a UG flash deck, you can play this and put the counters on a flier. Most common play pattern is probably to put counters on a mana dork you used to cast this, but even then you are attacking for 9 vs 11 (assuming a mana dork in both cases), and every turn after that you are attacking for at least as much.
Carnage Tyrant is definitely better against pure control, thanks to uncounterable and trample, but this isn't bad either. The opponent cannot just play draw-go, or this flips, and the only cards that kill it but not the Tyrant are Languish and the wildfires, none of which I have.
Of course, it also works in the Persist deck, which is in its colours.