As opposed to Mario games with all their clever level design and hidden secret areas all over, Sonic games are more about quantity, especially since the tempo is so much higher
I know you didn't grow up with mega drive but I though you had noticed that the levels actually are well planned! (Of course I'm talking about the first game here, haven't played so troughoutly with 2 and 3+S&K while thinking about design)
Every zone is designed to give a certain degree of challenge depending on which route you choose, and you're always allowed to change to another one at either possible crosspoints or by clever use of certain traps, their difficulties to access depends totally on the player experience and how secret/usefull they are!
Like that one hidden exit at Spring yard zone act2, most players simply rush by it without noticing its existance and to access it you must jump with good timing from a certain angle on the previous ramp. (You need to know the physics quite well to make it
Or maybe how greenhill zone is built, thought about what the developers had in mind?
Speed, yes but also to prove the capability of the physics engine and give the players 3 zones with slightly increasingly difficulty as a tutorial!
(And do not ever forget the feeling of freedom you have over choosing your own path along the way, thats a part of the tutorial!
On a side note, quantity of what?
There are only 19 levels in sonic aside from the additional 7 bonus stages compared to the many levels of the mario games
Do you really want to challenge me when it comes to sonic level design?
Anyway, enough about my reaction on the above.
You have to remember that there are many different types of difficulty we are talking about here, we have the plain factors from how the level looks with traps and areas that require some knowledge on how to reach, the enemies placement and direction as well as their different abilites and cleverness etc...
(There is also the player factor that I will leave uncommented for know, or so I thought...
All this have to be valued against each other and seen in combination at different times, views and places!
That might give you a total sum of the average difficulty, but I'm not sure since I just lost my own thread here...