I had the same issue as others with not being able to select either elven civ despite beating the Splintered Court.
I like that the starting island is big enough that you can conceivably complete the scenario without expanding onto other continents, but small enough to create a real incentive for settling cities you have to defend.
Regarding national units, are you supposed to be able to build 4 for each civ type (e.g., 4 lanun knights, 4 hippus knights, etc.)? I didn't really get to play with this since Stygians were working so well, but am seriously considering replaying this scenario on Immortal or (*shudder*) Diety.
I thought it would be cool to have other objectives on the map to discover, e.g. another civ you could find any ally with provided you rescue them from one of Tebryn's cronies. Or even a source of healing salves to patch up those human units. You know, something to make it feel like you have to look around and unravel the 'secrets' of the Black Tower rather than just a straight contest of arms.
Overall this was a terrific scenario. My tier 3 units have never feared Pyre Zombies like that before!