Overall I think that this is a good adventure that provides some challenge to high tier parties. Obviously at this level the power levels of groups varies widely and any adventure is going to require adjustments up or down depending on the group. This adventure provides a good baseline to work from.
Environmental challenges are a good way to drain some resources from a high tier group and they are present in abundance. However, some of the encounters that combine with these might have been better off designed as traps given the insanely low CR for tier 4 of some of the creatures used. They didn’t even make for a speed bump.
On the other hand, the final encounter did provide for some suspense as even tier 4 characters are in some danger from what was awaiting them.
[4 of 5 Stars!]