I bought it during the autumn sale and banged away at it for a few weeks. It's got a lot of different options to play with but I'd say it's more broad than deep. I picked it up around the same time as I got Frostpunk, Interplanetary, and the Civ VI expansion and I didn't end up spending a lot of time with Mars for Frostpunk. I'd say of the four, Interplanetary is the one I've played and enjoyed the most (something about annihilating cities with asteroids just appeals I suppose....)
Mars was just a little to dry and sterile for my liking. I understand that it's had a fair number of patches since I last fired it up so play dynamics might well have changed quite a bit since then. It is a Paradox game and they seem more willing than other companies to radically alter gameplay as time goes by.