Tekken's Fight System
Unlike most fighting games that focus on each button determines the strength of the punch or kick, Tekken focuses on attacking with one corresponding limb. Square was left punch, Triangle was right punch, X was left kick and Circle was right kick which in a way, made them like a puppet. At first I thought it strange but for some reason, it works like a charm. It did somehow allow the system to be masher friendly and more accessible. Another feature of Tekken is the inability to jump that high to change one's position to facing the opposite direction. Later on, this concept was transported for Mortal Kombat 2011's punch/kick system as well.
Tekken 3 featured the sidestepping move, which was more or less still in its rough development. The rough version of sidestepping was taken over in Tekken Tag Tournament. Tekken Tag Tournament featured a much different tag system where losing one character is all it takes to win or lose a round.
In Tekken 4, sidestepping was so easy that it was nerfing the pros plus uneven terrain was a problem. Uneven terrain is a problem which was fortunately corrected in Tekken 5 and onwards. So far Tekken has become more accessible and masher friendly without getting rid of depth.