If you love Age of Empires, then there's really no reason not to love this. Cossacks took almost everything that was great about Age of Kings and stuck it in a unique 17th/18th century setting, with significant improvements such as the capacity for hundreds of thousands of units and more tactical combat.
This is easily the best online FPS game i've ever played, and i've played a lot of them over the years - though admittedly the community has diminished, so it would be wrong of me to suggest that someone picking up the game for the first time today would have the same wonderful experiences i've had over the past decade. There's still fun to be had though if you find the right servers (multiplayer servers are still accessible via the regular CD version of the game, so i'm not sure why they wouldn't be via GoG's digital version). The single-player portion of the game hasn't aged well mostly due to simplistic AI, but it's still kind of fun if you can get the game cheap.
Perhaps one of the best RTS games of all time for base building with some very enjoyable singleplayer campaign missions. Don't expect great combat though.
