moxBorealis I'm working on an action adventure game at the moment, inspired by the Gameboy era Legend of Zelda games (Links Awakening, Oracle of Seasons).
For me, classic platforming is all about the learning curve. Give your players a toolset that they are introduced to over time, but let them play and experiment with it and reward them for it. Case in point, Super Mario world introduces the feather powerup which gives Mario the ability to fly. This allows the player to go back to earlier levels and discover secret areas and hidden pathways, bringing a whole new level of depth to the game world and actively encouraging the player to explore even more.
Also, it's very important for a platformer to use themes for different levels. These themes give the player a clue as to what enemies they will encounter, as well as other environmental hazards. Taking that a step back again, music is also key. As soon as I hear the cave theme from SMW I automatically know the list of enemies I'll have to deal with, and that there'll probably be lava, and most likely a cool secret room to find too.
My archetype list would be:
1. Super Mario World
2. Sonic The Hedgehog 2
3. Castlevania 2
4. Megaman series
5. Metroid series
I'm sure there are more, but I can't think of any right now.