How does the environment come into play?
1. You can turn off the lights in some missions. This reduces visibility and ranged hit chance obviously.
But if you then use a flash-bang grenade in darkness, the enemies will get not just blinded but also confused (attacking random targets).
2. There are a lot of exploadable objects. In some places, like gas stations, it can lead to whole chain reactions.
Flaming spoon cultist have a buff that makes their corpses explode, this can be used very creatively.
3. An explosion pushes aside everyone within 3 squares. If a character is pushed against a solid object or another character, he is stunned.
4. There's some interaction between elements.
Like hitting someone standing in water with lightning damage would additionally shock him; or ice damage putting out fires.
5. There's both cover (half-cover, full-cover) and concealment from bushes and smoke.