I think one can judge quality even allowing for 'early days'. For one thing, there is variation within AD&D products of the time, and even EGG-written AD&D products of the time.
Further, other contemporary games (Traveller and RuneQuest being the other two of the 'big three' triumvirate of the time) managed to produce adventure material that combined ease of use with interesting material and flexibility, so these aren't qualities that only came about recently.
One thing I would say from a *design* perspective is that I always found *all* of EGG's modules difficult to navigate since he tended to block out room/encounter descriptions all as one fat paragraph (making it hard to pick out at a glance creature tactics, descriptions and secrets etc.) , and in some cases (Against the Giants being the one that sticks in my mind) misses out all but hit points in monster stat blocks, making a trip to the MM inevitable (annoying on some occasions).