I admit, I'm a little behind, but still: great news!
I won't say I had enough experience facing him to think he was actually broken, but there certainly were several things I disliked about him after my first time facing him, especially while using Neverborn. Given that even the poster described them as overdue, I don't think I'm alone here.
For the most part, these are a thing of the past. Let's see what changed:
Indiscriminant Void is much simpler, and I believe was changed to stop some funky interactions with other models. I'm not sure, but I don't think it'll change his play a whole lot. Instead of him being placed and sacrificing a Stolen, the Stolen is just sacrificed, Hamelin stays put, and heals up.
Nihilism is basically an aura now, which is awesome, but hurts him a little, because now he'll have to be near the objectives in order to claim them- the rats can't do it themselves.
Bully was taken away, and replaced with Ruffian, which is a badly needed balance mechanism- now Gremlins and the like CAN target Hamelin, they just have to pass a WP -> 13 duel to do so.
Fate is Meaningless (Model ignores any modifiers to its flips during its next action) was turned into a (1) action (formerly (0)). I feel like this probably wasn't needed, especially since Useless Toy is still a (0) action, and overall probably more useful.
Haunting Melody changed to Wp->14 Duel is helpful, going against the Combat Duel total could have really sucked.
Overall, seems like a decent set of changes, at the very least making him a 'reasonable' matchup for Gremlins, plus a lot of other nice things to keep him in check.
Nix also gets the Nihilism aura, which again, is a nice balance mechanism, and gives Hamelin a way to win scenarios without necessarily being RIGHT THERE. Sweet Taste of Failure also only works on enemy models- a pretty nice change, since you generally aren't worried about Malifaux Rats failing duels, therefore Nix has to get close to use it.
Abandon has been removed from the Stolen. No longer can they make a model insignificant for basically no cost to the Hamelin crew (since he can create Stolen with a (1) action).
I've not seen the Rat-Catcher in action, but he's changed to be no longer Insignificant, but allowed to be added to Hamelin's crew via Affinity, and now, instead of freely killing Rats (which would give them infinite activations!), he can make them lose Slow. Still, a really nice ability for rats, but no longer feeling sort of ridiculous.
The Malifaux Rat, I felt, was the biggest problem with the Hamelin crew. They've changed quite a bit. No more -Wp combat trigger for them. No more Instinctual. No free positive flip modifier. No more ability to remove Corpse and Scrap counters (why?). Instead, if an enemy model is in contact with 3 or more Malifaux Rats, that model is -2 Df and -2 Wp. This still has a very thematic feel (swarms of rats slowing your opponent down), but is not a permanent effect. Also, combined with the Rat-Catcher, players will still get a lot of mileage out of the Rats and get more attacks, I'm guessing. The biggest change, for me, is their new rule: They're Just Rats. Other friendly models can't bring them to less than 1 WD, and can't be Summoned again if killed during it's own activation. Black Blood now kills rats dead! No more infinite activations! Huzzah! Seriously though, I feel this is a fantastic improvement.
Overall, it looks like Hamelin DOES maintain his feel and style (which is what made Rob interested in him anyway), but made him more in line with other Masters in the game. Truthfully, seems like very good changes, and certainly for the good of the game.