PSPo's gameplay is identical to PSU's. Apart from balance adjustments and extra content (such as PAs and whatnot), the games are mechanically the same.
Personally I'm surprised people aren't fans of the chaining system and the character PP system, I vastly prefer them to PSU's/PSPo's combat system as I personally found the game being reduced to infinite PP PA spam rather boring. The fact that chains are shared between groups made the system even more interesting I think, as the game emphasised teamwork over every man simply doing as much DPS as they can. The introduction of the multi-hit techniques in Infinity fixed all the problems I had with the chaining system, as you didn't have to necessarily "build up" on everything (and when you did build up, it was a lot faster), and weaker stuff could just be killed outright with an active Foverse.
I tried out PSU since the private server is up as well, but I personally couldn't get into it in comparison to Infinity. The game was a little too simple and mindless, I think. I feel the original PSO had more depth to it than PSU, which is a game I put thousands of hours into in the past.