iirc I recall first beating a very obscure game called Porky Pig's Haunted Holiday, pretty mediocre game looking back at it at this time considering the rest of the side scrollers out there, but for a game you can give out to a kid to play, it was alright, I used to play it all the time and found out every single area, I had no life, considering I didn't have many video games as a kid.
Yes, in fact I do not consider a game really beaten if it's not 100% completed (or more than that, many games back then used the over 100% gimmick, good times), the Crash Bandicoot, Spyro trilogies come to mind, Pacman World is another one, I recall always trying to get 100% on various Doom levels (though some of these are impossible to do without cheating due to badly marked secret sectors), Donkey Kong Country trilogy, and many others I can't seem to pop back in my head, if it keeps track of completion, I'll most likely do it, provided it's just not tedious.