There is a lot of nostalgia for IV recently among the vocal dissenters. And I personally can't go back to watch old IV matches let alone play. Just remembering the backdashes, OSes, plinking, vortexes and ultras and focus attacks tick me off a bit.
Gameplay wise this is great, it's high damage, fast paced, and easier to understand. The main thing is online is wonky in terms of matchmaking especially and the balance while not terrible is still not incentivizing more people to play a good chunk of the cast. I feel like I play the same kind of chars online that I see in top 16 in tournaments. Few play Rashid, Birdie, FANG, Guile, Claw, Sim. And the only Giefs are the high rank masochists.
And not having a set schedule of updates and the radio silence doesn't help. But for me, the main thing is just the online. Matchmaking, reworked battle lounge searches, and a better rage quit solution would be huge