Millhouse is stupidly broken. He went from last place to first place in the hero win rate.
I'm sure they'll figure out some way to fix him.
I think I'm usually Tier 6 at 9 mana with him, which is probably the norm for everyone using him that knows how to use him.
They also need to fix Bob's Tavern somehow, that Nozdormu is #2 or #3 in win rate is kind of a sign that is getting total crap in the Tavern is a problem. Sometimes when I go Tier 5, Bob gives me a whole ton of trash unit from the low tiers or awkward units nearly every re-roll.
I don't know how they can fix it, but the most successful heros right now other than Milhouse are ones that don't depend so heavily on the Tavern (Van Cleef, because he can buff any Tavern garbage, Rafaam because extra units, Toki because of Cheating, Alexstraza/AFK/Elise because of discover, Ysera with the free dragons, Pyramad who can also buff garbage, )
Tier upgrades any more can be semi-dangerous because it reduces the probability of Triples and Bob's Tavern is dangerously bad. And it feels like the probability of your Triple discover being Trash is too high as well. There are just too many bad units in Tier 4 or Tier 5 right now.