Ogame
Impossible to 'Win' but really fun in the long run imo. I'm on uni 35 TaroT.
Basic rundown: Menu Based RTS. Can be the super power of the universe with a fleet numbering in the thousands or a uber-turtle with defenses that can't be touched even by a deathstar.
I'm going for turtle with my friend on Uni 35 as it runs 5x speed. Not in the literal sense, it's just resource gathering and such happen 5x faster. I don't have to level my mines up as much to get say 5000 metal/h.