Pros:

The questing for keys and whatnot was fun and refreshing. Not just a point and shoot campaign.
Nice detail, and interesting maps. Lots to look at and get distracted with.

Cons:

The sewer maps were too long, and get dull if playing one person with three cpus. 
Easy to get lost, and not enough hints of where to go. It's fun to have a little mystery, but once frustrations sets in it stops being fun. 

Conclusion:

I didn't find the number of specials, or the difficulty at the end, to be that much of a problem. In fact, I found the extra challenge a lot more fun. There are a *lot* of specials.
Overall, this is one of the best maps I've played and it's in my regular rotation. I skip the sewer levels, only because they get dull with the long distance fetching, otherwise it's very fun.