I've never played platformers and bought the Manhattan project and am quite enjoying it, didn't know I would. Do you have recommendations for others? They always struck me as "kiddy" games. So steer me away from those unless that is a wrong assessment of the genre.

For example: Alien Rampage (DOS, if you want, I can make a DOSBoxed version for you of shareware), Bionic Commando: Rearmed, ARES (on Steam), Vigilante on Talos V (DOS), Earhworm Jim (on GOG - despite kiddy looks, a really fun and challenging game), Iron Blood (DOS), Vinyl Goddess from Mars (DOS), Guimo (DOS/Win9x), Abuse...

There not on GoG but Duke Nukem 1 and 2 are great side scrollers.