In no particular order:
1. The module was about five years late. Notwithstanding that, it wasn't even finished. It was up to the DM to populate the elemental nodes. I would have preferred that EGG (or whoever the author was that was working from his rough notes) had put some effort into making these into coherent sites rather than the cheap "it's over to you, DM"-tactic that was employed in order to rush this into publication.
2. I would have thought that five years was long enough to make the clerics feel other than generic. I fully expected to see a water cleric, frex, with some water-based spells to differentiate him from the, frex, earth cleric. (Again, I know a DM can change the flavour etc... but sometimes I actually buy an adventure so that the work is done for me.)
3. Five years to design a giant dungeon crawl of seemingly randomly generated monsters?
In short, it lack any sense of coherency and simply didn't do justice to its theme. It also destroyed AD&D for one of my groups: giant dungeons just didn't (and don't) work for us.
It would have been better written up as five separate sites: one for each of the elements plus a main temple in the centre and wilderness adventures in-between. Actually, it would have been better if it had been finished on time and not slapped together at the last minute to try and get sales from the EGG name.