OpenRA

many new players.
Read this, and do not send lone engineers...

imma defensive player? Perhaps but,

"Players like Overkill, Mamers, and Bellator like to play defensively, building up their base and defenses and conquering the map forcing the other player to run out of resources and then finally, using Super Weapons (Chronosphere/Nuke) To destroy the player later into the game. "

I never use super weapons.

How to watch downloaded replays on OS X version?

I'm stuck on this shitty OS so I can help you.

Put the replay inside this folder:
/Users/<username>/Library/Application Support/OpenRA/Replays/

Then they should show up in OpenRA in the replays menu.