Yeah, demon negotiations were pretty cool. Although it's quite easy to start farming tarot cards, or cheat the system, if you memorize the patterns for the different demon types

which is one of the reasons I prefer S. Links as a feature in 3/4 (sometimes it's referred to as the replacement for negotiations, since it does take some inspiration from certain aspects of it).
I completely agree. It's not that it's a bad system, it's just that 3/4 uses a much better one. Though sometimes I find myself preferring P2's battle system (the PSP remake's, of course, as it got a huge improvement to the UI) over P3's, because having the AI control your party members can sometimes be a pain (for example, when you're at extremely low HP, but one hit away from beating Nyx, and Mitsuru decides to use Marin Karin instead of heal you and you have to restart the entire damn fight over).
For sure, take your time. It's definitely worth finishing.
Ah, I've seen that video

thanks for reminding me of it.
It's highly informative, and the directors look pretty damn badass