I've gone through Persona, Eternal Punishment, Innocent Sin, P3FES and P4. I wouldn't recommend Persona or the Persona 2 games to someone who enjoyed Persona 3 or 4 unless they also love more old-school style JRPGs with the usual degree of tedious yet somehow satisfying grinding. It's a unique experience, with quirky characters and an outrageous but fascinating plot in a modern urban setting, but it doesn't have any of the visual novel gameplay which makes P3/4 so engrossing.
I love the negotiating with the demons in particular - all the standard random encounter monsters you meet can be either fought or reasoned with for items or support - doing so can be challenging and hilarious as it breaks through the monotony of blowing them away.