I left a bunch of questions blank because I haven’t played many heroes or any of the paywalled content, but I answered what I could. Comments below for my “other” answers.
Stagger: when heroes are clustered fighting the same enemies, the bonus damage feels too strong. When heroes are separated fighting different groups of enemies alone, the higher HP values meant to compensate for the stagger bonus are just annoying. This system makes heroes both too strong and too weak (and is overly complicated /etc.) and should just be cut.
Beastmen: way too common. Horde size isn’t necessarily too large, but it feels like there are hardly any classic Chaos/Skaven enemies on the maps now.