I started off in O scale 17 years ago, started a much too ambitious layout, tore it up after a couple years thinking O was too challenging. Then tried all the smaller scales, N, TT, HO, OO, and attempted to build half a dozen layouts, only to become dissatisfied with them, thinking I'd chosen the wrong prototype, railway company etc... and starting again.
Back in 2016, my Dad purchased a Dapol O gauge Terrier, he couldn't resist it due to the low price. Package arrived from the UK while he was away and he instructed me to go ahead and open it up and have a look. Once the loco was out of the box, I knew that was it ! Eureka
In my opinion with O, you get the feeling of the real thing, due to the size / weight, not to mention detail + the figures look like real characters you'd see or maybe even remember from your youth.
In HO / OO, I felt like I was shunting little pieces of plastic around the goods yard, in O, I get the feeling of shunting wagons around the goods yard
Once you experience O, you can't go back, at least for me, sadly it took 17 years to realize that !