Jagged Alliance 2 (especially with the 1.13 mod) is the most ludicrously detailed tactical RPG you’ll ever find. It can be a nightmare to actually play until you spend many, many hours learning all its systems, but nothing else comes close immersion-wise. You can customize every mercenary’s loadout down to individual weapon attachments, capturing different parts of the map gives bonuses that actually make sense (like being able to ship in weapons once you’ve taken the airport), you can train militias to hold onto captured sectors for you, and you can even use the in-game internet to send flowers to the main villain.