time-demanding level
Aigis is a non-competitive game. Completely single player. You can take it entirely at your own pace, or you can try and keep up with events. Which right now is very easy to do.
At first, you can sit and play quite a bit, but once you start gaining levels, you get more time to sit and wait for char to regenerate.

recommended system/browser
I play in chrome. I don't freeze or crash ever, but it does slowdown a bit outside of maps. Disable hardware acceleration if you are having too much issues. I've also played in Opera, which is much smoother - but recently both in and out of maps, I've been occasionally unable to select anything, or place units. As if it wasn't registering my clicks.