With a scanned product, there can be technical issues over its legibility. However, with this product, the problem seems primarily to have been with the original printed version, not how it was scanned. Dark grey print on a mottled grey background was probably never easy to read in a hard-copy book. It hasn't been improved by its electronic recreation here!
The text does though remain generally legible, barring a few places where you may have to guess, both on-screen and in printout forms, and the information in the book, including its colour maps, is essentially unique for this heavily ice-covered, frozen part of the D&D "Forgotten Realms" world. The setting is perhaps overly human-centric, with few new creatures presented, and just humans and arctic dwarves as races in this isolated region (so no orcs, a little odd, given how they thrive in hordes across much of the less-icy northern Forgotten Realm lands elsewhere).
Possibly too remote and cold a location for many gamers (maybe why the region seems never to have been revisited by subsequent editions of D&D), the excellent level and quantity of unique information in "The Great Glacier" easily warrants a 5-star rating. However, the difficulties in reading it because of its muddy original printing promote merely a 1-star view. Hence I've opted, in true D&D 5e form, for the mean in rating it here.