Back in the day, when sonic first came out on the Genesis, I picked up the console to check it out.
I have to say that Sonic 1 was a good game and it served a purpose to me back then ... it was a relief from the intense and unforgiving platforming offered in the Mario games I had at the time which were Super Mario Bros, Super Mario Bros 3, and Super Mario World.
Sonic's moves where much more basic than Mario's moves ... he could walk, run, and turn into a ball and roll ... that was it. So it was easier to deal with Sonic than Mario and the platforming and enemies were easier than Mario as well. So it was the kind of game you could relax while you played it.
Sonic 1 offered just enough platforming challenge not to be too easy but not enough challenge to get ultra frustrating. It offered a large character, size wise, than Mario and it was a brighter, cheerier game as well. Sonic had personality too ... if you did not move him, he would tap his foot (a big deal back in the day) The special stages in Sonic 1 were awesome ... with the level turning and having to make your way to the chaos emerald without falling into an exit ... it was very visually stimulating and advanced for its time .. in my opinion, the best special stage of any Sonic game.
To me, it seemed like a great start for a series ... then when Sonic 2 came out I got that too. Immediately I realized that the graphics were more muddy than Sonic 1 and the gameplay was headed down hill ... the spin dash helped you rev up speed so you didn't have to walk back to pick up speed to make it through a loop, a nice touch but the problem was, it turned into a loop da loop game and was less of a platformer than Sonic 1. It was riddled with cheap deaths caused by speeding up and then running into an enemy you could not see until after he had already killed you.
Instead of Sonic growing up and obtaining new good moves, he was falling apart as a platformer and becoming a racing game.
After Sonic 3, I had had enough with Sonic and had no interest in buying another Sega Console. I said to myself ... If I don't like their Mascot games, which are supposed to be their flagship games, what else is there?
From the very start, Mario was a better platformer, the best actually, starting with Super Mario Bros. It had very tight controls, tons of secret things in it (hidden blocks, veins, secret exits), and it had great power ups too ...
The thing is, because Mario was so good and had done things right with regard to gameplay mechanics, moves, and power ups, it destroyed the chances of any other platformer that would come after it. Mario already had the right moves so anyone else who copied those moves would be in trouble for outright copying Mario. So developers would have to scratch their heads thinking ... how can we make a platformer that is not Mario? The problem is, you really can't come up with a great platformer that does not borrow from Mario and if you get too close to his moves and the mechanics of his enemies, you run the risk of being in trouble for copying Mario. This is why Mario, even to this day is the best platformer.
As Sonic's moves got worse over time, Mario's moves just got better and better. Nintendo had the perfect platformer to start with but amazingly, they kept adding additional moves to Mario that perfected perfection. At first Mario only walked, ran, jumped, became bigger, and got power ups that allowed him to shoot fire balls and become invincible. As time went on, he was able to backtrack in a level, wall jump, fly, glide, butt stomp, and now climb walls as a cat and multiply himself!
The thing is, when each new ability for Mario debuts, it is done perfectly and you get the sense that he was always made to do the new thing he is doing ... its natural. We have become so accustomed to his new moves that it is easy to forget there was a time he did not have them ... go back an play Super Mario Bros and tell me if you don't screw up because you think you can back track, butt stop, or wall jump ....
Generally, with each new game, Mario gets better and better adding new moves to a repertoire which has already been rock solid from day one ... and it is because of this that no one has been able to match the great gameplay found in Mario games .... he has always had the moves and is constantly adding new ones that work, thereby making it even harder for other developers to keep up or outdo him.
Sonic will always be at a loss, Mario already has the moves. Sonic can try elements that Mario has already accomplished to improve its game such as 360 play fields (Mario Galaxy) But Sonic Will Always Be In A Lost World because Mario will always be King, he was just born with the right moves.