This was the first 'modern' Commander Keen game, and is fondly remembered by people of a certain age. Whilst the first three games had tiny sprites and decent, but uninspired gameplay, this and the follow-ups were excellent and are still fun today (certainly the most fun you can have on a PC with just 700k).
The mixture of Mario-esque gameplay, a pogo stick, some utterly cheesy Adlib music, and an engaging amateurishness fits together perfectly. The difficulty level is pitched perfectly, too - it gets progressively harder, but deceptively so, and although you can save and load as often as you like, you tend not to as it all seems initially simple.
For what it is, this game is perfect - Nintendo-style platform games are extremely rare on the PC, and the cute graphics and bouncy music haven't really dated (compared to something like 'Puzzle Bobble' they're positively advanced).
The Bottom Line
A fun, nostalgic early-90's PC-based shareware platformer by soon-to-be-Doomsters.