I like this on reading. A medium-sized, very-strongly-themed dungeoncrawl with the potential for faction play with several different groups of (evil) cultists showing up after the players enter. Creative treasure, particularly interesting consumable magic. One nearby probably-hostile settlement briefly sketched. The separate player-facing map is quite appropriate: of high enough resolution & detail for oldschool play; fancier than dungeonscrawler output, but not as unreadably cluttered or illegibly shaded as you find with a lot of commercial 5e maps. The "Continuing & Concluding the Adventure" section isn't an explicit timeline but it has a really nice spread of discussion of faction goals & possible evolutions, ties to nearby parts of the world.

Downsides: really verbose, hints of quantum ogres (the competitive factions explicitly scale with party level), and perhaps a bit too on the nose with the elemental theming - the vast majority of the native opposition is "two mephits of (appropriate quasielemental subtype)".

I'm not sure about the skill checks - there sure are a lot of them, but then players having advantage on knowledge checks from their background ought to be really common, so there's not too much information hiding or "roll to make progress", and the range of physical DCs seems reasonable.

Nits: both the terrain map and the dungeon map in the book have critical material in the center of the page - which means it's cut by the "gutter" of the book layout, and thus really hard to read. Art is really mixed stylistically and varying in quality, so for every piece I'd be happy to show my players there are two I wouldn't.

The 4/5 rating assumes you're playing Swords of Kos or a generic anything-goes D&D setting. I'd give this only 3/5 in any of the other pseudo-Greek settings - the shrine is particularly wedded to a Gygaxian inner planes and the Swords of Kos cosmology, and there'll be a lot of work to drop this in another world cleanly. For example, Arkadia has four great titans, but they don't line up so cleanly with the elements, there's not a lot of support for paraelemental lesser titans, the geographic associations of the titans are different which pushes one to rearrange the dungeon, redrawing the map; this in turn suggests replacing at least some of the mephits, etc... Even less of a clear fit for Theros or Thylea.

Preliminary review; will update if I can get my players to head toward where I've dropped this into the world map.