I think this is one of those things to get your head around the most. FF games create amazing worlds to go and run around in, no matter the era or graphics. ATB was just the ticket when FF7 came out on the Playstation way back then. For kids like me growing up it got you thinking a little like playing chess but in a more intense gaming arena. Unfortunately for me, I enjoyed this way so much that when i picked up a few later in the series ( it was 13 i believe) I just couldn't get on with the Unique Battle System. It is the one thing i'm overly notlooking forward to when i play the FF7 remake even if you have ATB options rolled into it.
I'd also say that the Summons were the most amazing things ever back in 7 and 8. Create a mini movie scene with each fight, even if its a weak chocobo was just hilarious to use and the animations on how each Summon worked were very unique.
I've never played anything before 7 but I probably should try. The only thing to realise is that FF games are usually on the grindy side, especially early ones because Japan were heavily into that way of gaming in those days - so you need to put some time aside to get through them. I'm shamed to admit that I have played FF7 and FF8 for hours on end, yet i never completed them. Never say never though.