I stopped playing playing Dungeons and Dragons for 8 years from 1998 to 2005. I remember when I came back it was very jarring to see the "weird" 5-ft. scale maps. I think 3.5e was made specifically for use with miniatures. I think 3e had a section in the back showing us how to play with minotaurs. Before 1998 I never played with miniatures.
I used a lot of gridded maps back in 1E & B/X, having gotten miniatures literally the day after I got my first D&D books. Though the maps in those modules favored drawing things out in 10 ft. squares. I remember getting frustrated with other RPGs back in that time that didn't have gridded maps (like Villains & Vigilantes).
2E's Combat & Tactics had a large section on gridded combat, so way before 3E. There were several 2E (and 1E) modules released (such as the Greyhawk Falconmaster adventures) that came with gridded battlemats for miniature-based play.
The 3E Miniatures Handbook was where that edition started moving towards pushing the grid, especially with the pre-painted miniatures were coming out. As I remember 3.5E came out shortly after the Miniatures Handbook and started doubling down on miniature use.
On topic, multiple paths - even if secret paths - make big differences in the map layout. However, those alternate paths tie in strongly to how the dungeon is stocked - if it's a coin flip for which path to choose instead of being able to making informed decisions (even if the information is incomplete), there's little to no excitement in choosing one path over another.
As others have mentioned, throwing in terrain - even if its as mundane as tables, chairs, torture equipment, daises and other clutter that breaks up a room from just being a bunch of 5 ft. blocks.
I'll also echo the "area you can see but can't immediately reach" is fun and interesting. My wife pulled this in one of the recent adventures, where we were on an upper level and could see the BBEG (talking) in the room below us, but had to find a path down to them made things interesting. It gave us an idea of who'd we be facing, but getting there was the majority of the challenge.
One of the least used tricks (at least in D&D) is the room that needs to be revisited after performing some action or acquiring some gear elsewhere.
Labyrinth of Madness from 2E used this
extensively, as do video games like the various Legend of Zelda games, but I haven't seen it in WotC adventure design since a long, long time ago.