These are some of the best levels for “Mario” that I've played. For one thing, each of these levels is very well made: no stones in seemingly random locations or large blocks missing from their tops. Each tile has its purpose. The readme also has a nice walkthrough of each level, with descriptions of the various hidden features. Most importantly, the gameplay is amazing! One of the things that I really liked about these worlds is that, unlike many other levels I've tried, the first level is beatable. All of the levels are reasonably beatable (no throw-the-calc-against-the-wall levels), but not too easy either (it'll take a few tries for each one), which makes them very addictive. You'll keep coming back to beat that one spot on Level 4 that you missed last time! It took me a couple days to finish each world, but it wasn't easy, and I was playing during all my free time! Altogether, these levels are just a little on the easy side, but that's fixed in worlds 3 and 4 of this author’s series. I highly recommend these levels!