Though not revolutionary for their time, the Earthworm Jim games provided a solid platforming experience with a heavy dose of personality, enough that managed to spawn a successful animated series, a toy line, and a(somewhat dissapointing) 3rd game in the series, as well as more recent ports to the Gameboy Advance.
The basic mechanics of Earthworm Jim are a combination of platformers and shooters, with an emphasis on the platforming aspect. Jim has a wide array of weaponry available to him with various effects, from simple things like the essential tri-beam spread shot type weapons, to more outlandish things like the Barn Blaster, which has incredibly limited ammo and can one-shot every enemy on screen at the same time.
However, the games frequently deviate from the typical levels and keep things interesting, introducing minigames or vastly different mechanics to deal with. At times, these can be frustrating to players(especially in the first game), but they keep the game interesting when it could have otherwise begun to slip into monotony.
The PC versions are widely considered an improvement on the console versions of the EWJ games, having higher quality music and additional content that goes beyond adding an extra level or weapon here or there. Even if you've got the original games on the Super Nintendo or the Sega Genesis, it's worth getting them on the PC for the low price GoG.com offers.
With the franchise poised to be revived through not only a new game, but a new animated series and potential movie, now is as good a time as any to get the original Earthworm Jim games, and relive some classic and humor-filled gaming of the 16-bit era.