This mission is one of the best ones featuring the Hammers I've played so far. While the story is nothing groundbreaking, it is well written and pretty decent so no complaints there, and the atmosphere is also great. Two things have lessend my enjoyment of the gameplay, though.

First and foremost, I believe a map would've been VERY helpful as the fortress is quite big and can get frustrating to navigate, especially when you're looking for a specific thing and can't quite remember exactly how to get there so you spend a good few minutes running in circles. It's not a huge problem though and I realize that most people will probably have a better sense of direction than me.
But the frustration of having no map is exacerbated further by the rather hefty amount of loot required for the gold objective. I was pretty close to calling it a day because I was still some gold short, but then I found a hidden safe tucked away behind one of the many banners.

Nonetheless, it's a great mission and as long as you pay attention to your surroundings there's around one and a half hours of enjoyment to be found here.

I can only echo what you wrote. This is a great mission, but, it sorely lacks a map (not just because the Hammerite fortress is pretty difficult to navigate, but, especially because you will probably take the armory key pretty early from a guard, and then you stumble around the fortress without knowing where the armory actually is. In my case, I probably explored 90% of the fortress, until I finally managed to find the armory, and had to backtrack to places where banners or high beams were, where loot could be hidden).

And, yes, the loot requirement is way too high as well. I had to consult a walkthrough video of the mission to be able to make the cut... It's at least 400 gold too high.

So, for me, it's also 8/10, which could have been a 9/10, without the two major issues it has. Still a lot of fun, of course.