Battle for Wesnoth is absolutely epic. I played it over a decade ago, and it a brilliant story and many great, epic battles. I have no idea what they added since then, but it's probably worth checking out.

Battle for Wesnoth is like the Blender or Firefox of open source games, in the "I can't believe something could have this much polish and not be a commercial product" sense. It is really well done.

Upvoting for Battle of Wesnoth. It's a great game and feels rewarding to succeed at. It's got a great ecosystem of addons, such as user submitted stories that you play along, so there's a plenty of content to explore.

I just installed the Kittens game on my phone. That may have been a mistake. I am already hooked.