Definitely have to recommend Bike Rider DX2.
The first Bike Rider DX was THE #1 top selling eShop-exclusive game in Japan for all of 2013, even outselling Pokemon Dream Radar. I bought it thinking that all of those people couldn't be wrong, and that thinking was correct. It was great.
Bike Rider DX2 outdoes the first one in every way, to the point where the first game is mostly irrelevant (also, it easily made the Japan top 10 for 2014). Simple gameplay (move forward automatically, press button to jump, get the 3 medals and reach the goal). It has some of the best level design I've ever seen, plus great powerups, a ton of hidden levels, and a great soundtrack. In North America it's a whopping $3.
If you have a Japanese system, Bike Rider DX3 came out late last year...
Oh, and as for the Picross e series, only get those if you're willing to sacrifice every last shred of your free time, because those are addictive as hell, lol