After starting it six months ago, I finally beat Persona 4 yesterday. Easily some of the best characters ever, and now among my most favourite games.
Even though the battle system is what differentiates the Persona games, I think they need to make some changes for the next game. By the end of Persona 3: FES I was tired of battles. It was often so much easier and faster to take care of enemies myself in a single turn, so by the time I got to where I needed the SP for abilities, I was out or there was a significant dent in SP. But I believe the need to go to Tartarus to make sure your party was strong enough by the next full moon was what caused me to get tired of battles when I did (too much grinding).
With Persona 4, however, I only had to go into the TV twice (and sometimes once) to save the next victim. I never tired of battles and could get back to bettering my character or social links sooner. The tradeoff was that you could never do another activity when you got home. Sometimes I wish I could just stay up and study, regardless of whether or not I got sick (like in P3). With the combat being much the same, but less often and a little easier for the most part, I think Persona 5 needs to make some changes or risk stagnation.
I heard most players thought the plot seemed to weird out by the end, but I didn't find the good ending that bad.
The true ending, however, seemed a little out of left field.