I picked up Mini Metro using money I saved up by selling Steam cards. It is to city sims what rymdkapsel was to RTS: very low learning curve but a surprisingly complex game once things get rolling, with nice minimalist art that doesn’t overload you with tons of windows and overlays and info dumps. And most importantly for a sim game, it is stupid addictive. You can play in short (~15min) bursts with the daily challenge or by racking up enough points to unlock the next level, or you can go totally zen with endless mode.
I’ve unlocked all of the normal levels and played through them all at least once, and am now in the process of unlocking all of the extreme levels. This is the only part of the game that really makes me scratch my head, though. Why are the extreme levels locked behind achievements, rather than just being available from the start? Oh, well.
But for all of that, I really like it. It is good, and you should check it out.
(Damn. Now I want to go back and play rymdkapsel.)