Hmm... There's stuff that's 30 or 40MB and lots of fun
Risk of rain for example. It's small, not that laggy even if you do some crazy stuff (or I hope so at least) and very replayable. Even when you know how to play it there are a lot of ways to challenge yourself, or just play only to slash through all the things. Gotta buy it but it's not that expensive and definitely recommended.
Actually, this list is pretty good:
You might find something for yourself there. There are a couple of free things there too.
I hope I got the url right
