This mission is really detail-rich with a strong emphasis on vertical gameplay and opening up one-way passages.
The sheer complexity of the map layout however quickly tires, leading to walking the same passages again and again to make sure nothing of importance was missed. This quickly becomes time-consuming and the player should plan four, even better five hours to finish this mission. Often enemies are placed right around the corners, they are really strong and not easy to counter in the tight spaces of Tolham.
Overall a great mission by a very talented author (and I hope there will be many others fan missions to come), but a tough chunk to chew on.

I advise this mission only to experienced and very patient players.

I don't know about the 4-5 hours playtime, but I've played the mission on Normal and yeah, it took me ~2 hours (though technically I could finish it sooner, I just tried to explore optional areas), so with the additional objectives I can imagine that estimation is correct. The mission perhaps relies on the player collecting the scattered loot a bit too much.