I'll try breaking up my opinion of Tekken into categories.
Number of releases:
I agree that they sort of have too many games or too many variations of the same games. I sort of wish they just focused on having the main 1-6 and Tag games on more systems, instead of marketing them as so many different editions (like T5DR and T6BR) or turning them into spinoffs. For example: I wish Tekken 3D Prime Edition for 3DS was more of a direct port of PSP Tekken 6 and kept more of the same features as the PSP version.
Gameplay:
I mostly like Tekken 3 and Tag 1 as far as gameplay. After Tekken 4, it seems like there are to many moves and most of the moves are too similar. I'm just a casual player, but I think fewer move would make it easier to get better at using different characters. Back when there were fewer moves, I used to feel like routinely practicing a character's entire move set.
Characters/Story:
I think the Tekken stories have always been good so far, but I'm not sure if I like how the characters have changed in their personality or visual design. In some ways, it seems like they are trying too hard to make the characters look more tough instead of expressing other things about the characters.
Music:
I understand that people's tastes in music can vary widely, but here's my opinion. One of the things I like the most about the Tekken series is the music, but some of the recent soundtracks have been disappointing to me. I think music is an important part of the series since it makes long practice sessions more enjoyable by providing slightly relaxing music to practice to. I mostly like the soundtracks of Tekken 1 through 4. The newer soundtracks often sound too simple, hyper, or random to me.