The main mechanical difference from modern games, other than that, is the lack of fast travel—but it kinda does have it, it's just in-world. The three (? IIRC? Though admittedly one is a ton of work to get) fast travel networks, the mark and recall spells, and almsivi/divine intervention, between all those there pretty much is fast travel, it's just in-world rather than a meta thing you do on the world map.
Oh, and the lack of quest markers, I suppose. You do actually have to follow the directions people give you, to find things. But that's excellent and it's a shame they took that out of the later entries.
Four; silt striders, boats, and mages guild are straight forward, but propylon chamber are a pain in the ass.