1) Constant image changes. They don't have a set image like the once had. When you thought of TWICE, you thought of 9 girls with cheerful personalities and a bright, enjoyable concept to lift up your day. From Fancy onwards their image has been very confusing, with them going from bright but mature with Fancy/M&M/FS, to a much darker concept with CFM/ICSM, to a brighter concept with Alcohol-Free. There's just no consistency.
That's what Bts follows. Changing concepts each time which makes them interesting.