Just beat the story campaign for Tekken 8, and played several character episodes and some arcade matches. Granted, I haven't done everything yet but I have seen enough to give a review. Don't worry, I won't spoil any of the story mode.
The graphics are amazing. Big step up from Tekken 7. The story has some phenomenal fight scenes and has some moments that tie up the whole Jin vs Kazuya storyline that has been going on since Tekken 3. The story does focus almost exclusively on Jin and Kazuya though, but every character gets a brief moment in the story for some high jinks. It is a Tekken game so it has its humor and over the top fighting.
Namco took a page from Capcom and inserted an easy combo system that one can turn off and on. It doesn't simplify the controls so one still has to have an idea of which buttons to mash and control stick to spin, but some juggle combos and the new "heat"l mode" to use the rage arts and amplify attacks are easier to use when the system is turned on.
On to the negatives. Like everything else nowadays, dlc and battle passes are a thing. The fan service the series is known for has been dialed down hard. The men all have shirtless costumes, while most of the women just have nice dresses or shorts. Only the new gal, Azucena, has a swimsuit. She is clearly the Ms Fanservice for this game, at least for now (go modders go). The item options for character customization are much smaller than previous games, but I am assuming that will be taken care of by the aforementioned dlc and battle passes (as well as the lack of fan service).
I would say, if you are a Tekken fan like I am, get it. If not, wait till more of the dlc gets released then make up your mind then.
Yeah, the childish avatar crap is bad. It makes no sense to have it considering the character models walk around in 3d environments already.