The Decisive Campaigns titles are all great imo. They are developed by one dude for the most part and known for their good scenario design and decent to great AI.
Unfortunately they are also known for weird UIs, so if that kinda thing bothers you, I’d watch a video or something first to see if it’s something you want to spend some time learning.
Edit: The first one allows up to like 5 players in PBEM and its as fun as it sounds. I’ve played hundreds of hours of it with dudes from SA.