Sonic The Hedgehog:
Marble Zone:
I actually like the level, Greenhill Zone was all about speed which is a staple of the Sonic series (first zone always just speed), but the second one you have to learn to be patient, take your time and avoid danger. I never go for the caterpillars as they are just too risky.
Labyrinth Zone:
I had to do the L,R,U,D, A+Start to get passed the third stage. Once you have the routes understood it isn't too bad. The last boss ended me as a kid, was only when I was an adult I realised I didn't need to hit Robotnik but I had to just survive.
Scrap Brain Zone:
Act 1-2 is great, but 3 is such a shift back to the Labyrinth Zone. I am sure there was a route which got you to the Final zone very quickly but have never found it as an adult.
Final Zone:
Last Boss was awful, just hide at the side and jump now and again.
First Computer game I ever played (Got it with Mega Drive for Christmas and I still love it).
Sonic 2 Special Stage was the pits, awful it was all memory of each corner, but becoming Super Sonic was great.
Final Stage was amazing and without rings was very nerve racking!