Deus Ex, especially the first, actively rewards you with experience, items, and new missions if you explore. I can think of three unique areas / paths you can explore in the 2nd mission (Hell's Kitchen) just off the top of my head. And there's no question mark indicators on your map that anythings there - you have to seek it out.

It's not an "open world" but its level design is much more intricately layered than any part of CP2077, including the main mission set pieces. You can even kill important NPCs and it will change the storyline