Basically everyone will have their own subjective biases in terms of what sort of mechanics they would enjoy, or actively want in an ARPG. The perfect game only really exists temporarily. And a lot of people really don't even know what they want in an ARPG, but think they do. This being said, the direction I would take regarding the current state of Median;
Remove the Challenges. That is just a slap in the face to the pacing. I know Marco and the team know's this, I'm basically just saying I agree.
Make enemies that are capable of off screen attacks (Gothi, Manglers etc) deal moderately less damage. This keeps the challenge somewhat fair for ranged, but will be far less dangerous for melee builds, which are inherently going to take far more damage.
Make minions slightly tankier. Not because I think they're weak, but because the incessant re summoning is what turns most people off to the build. Either that, or give them far higher damage, so the summoner takes an active roll, and has to use summons like a spell; high damage, frequent casting. Although, who knows how i'd feel after trying it. Maybe summoners are just going to be inherently boring to some people, i dunno.
The idea of Barb Shaman is great, but setting him up as a hybrid summon/ melee is not something that will feel good, or be very effective at all.
RMB stances are a huge turn-off.
Witches do not add enjoyment to the game.