Options.
I'm thinking in an SP mindset, but this easily applies to MP as well. Instead of just one path, add multiple. Add a flanking route or two. Make sure your map has verticality. Use pushing areas/gravitators and water areas to help with that. Also, terrain should NEVER be flat.
Also, keep in mind with SP maps to make them easy for the AI to navigate if you are thinking about adding allies. I'm sure you know that the AI sucks at vertical pathfinding (and if you didn't, well now you know). That may mean less verticality, but the AI should be fine if you make the map so that all the different paths ultimately link up at this one point in the level. Each of these paths should be more or less horizontal (but NOT FLAT) so the AI doesn't get bamboozled. And if all else fails, just use a trigger that automatically teleports all of your allies to you.
Now that's not to say that you should go crazy and make your map gigantic. If you can make your map complex, with verticality and multiple pathways and all that, then there should be no reason to make your map super big. In SP, maps that are very big tend to take longer to complete especially if you are making them nonlinear. This makes it repetitive to play through, and players may give up after dying once or twice. Instead, it's better to make several smaller but good maps. Remember: rely on complexity, not size.
In MP, a super giant map that cannot be compensated by the player count is bad, as it will generally mean less action for players, and will probably encourage camping. Anyways, I'm not an MP mapmaker, so I don't dare to say much more on the matter. Just remember: complexity over size.
Finally, one last point is to make sure that walls overlap each other instead of just being right next to each other in order to prevent characters from glitching between them and getting turned to paste.
So that's it. I hope I answered your question. If not, then let me know.
If you want some cool looking terrain, then play some of Phelix's BH maps:
https://www.plazmaburst2.com/?s=9&a=&m= ... &id=862644I know they're last gen, but still, the terrain is beautiful, especially in the first few maps.
Or something more modern, then:
https://www.plazmaburst2.com/?s=9&a=&m= ... &id=952107And I'm sure you can find several more good examples by yourself.