Hello Wa666r. I finished your campaign on hard (got a playlist of it
here, but commentary is in french).
Overall, it was pretty great. I encountered a few bugs (including a freeze in the last mission).
For some reason, Zaq's name changed in the last mission, and he lost his third spell (the crack in the ground, don't remember the name of the skill).
Overall, I think the pacing and the difficulty were alright.
The hardest missions, IMO, were 7 (Unfathomable depths 2) and 10 (Gate of Azjol Nerub). In 7, the faceless are really, really strong. Their heavy unit's damage range is something like 80-110, which is insane. In comparison, the living Nerubians feel really weaker. As a matter of fact, the only way I found to beat the faceless was to pull them and bring them to the living nerubian base. While the two were fighting, I destroyed the faceless' base. I don't think I could have taken them head on with the units we have in this mission.
Mission 10 was hard too, mostly because, after a while it feels like you're constantly under attack by very powerful heroes. The two heroes from the left base, then two minutes later Anu'barak, then two minutes later the two heroes from the right base. Then five minutes later it starts again. I don't think I could have detroyed their base too, but tbh I never felt like I had enough time to even try.
In mission 11, oddly, the hardest base to destroy IMO was the Royal Guard base. That is because the two queen heroes are completely fubar. They create dozens upon dozens of spiders and they are relentless. Overall, I think the living nerubian heroes are either too weak (the Vizier and the guy with the sword, treasurer I think?) or really OP (the Queen and the guy who heals way faster than you can damage him). I also think the AI also has way too much siege damage, which makes towers (which aren't that great to begin with) completely useless: the long range scorpions, the long range flyers, the big armored dudes... I'm not a big fan of the invisible archers too, if only because they can one shot the monitor, which makes dealing with them really annoying.
I think the idea of introducing a challenge mode is nice and all, but to be honest, I don't feel like redoing some missions when they're even harder. I'm going through them with cheats, and I've already found some bugs. In mission 3, Zaq doesn't have his first spell (the stun). Even if you select it at level 4, it doesn't appear on your character. In mission 4, it says that you have to destroy two bases (light grey and green?), but all the living nerubians are red (same thing for the blue dragons), so heh? Edit: the same thing happens in mission 5: all AI factions are red, even the trolls.
Lastly, I think the campaign lacks some cool items. It's pretty much only vanilla items, except for a handful of stuff you can buy in the store. It's nice that challenge mode provides extra items, but a few additionnal ones in the regular campaign wouldn't hurt.