Combat-wise, Phantasy Star Online 2 is much, much more action-centric than PSO. I have some difficulties with the implementation (mainly dealing with subpalletes as a controller-user, and the camera being hot garbage), but it's generally fun and most people tend to favor it. The battle is PSO2AH an evolution of PSU's in how Photon Arts can be utilized while it maintains the Just-Attacks from PSO so that it does still feel attached. Weapon specials are normally pretty irrelevant now though, but a couple of firearms have potentials that try to provide a flavour that is similar. Essentially, in the event that you liked deliberate and slow that the battle in PSO felt, you're gonna have a poor moment. Otherwise, you'll probably find it much more fun.
While PSO would give you an instance of an incident and let you run through the whole thing in a linear fashion, PSO2 is based on individual missions. You then return back to the camp-ship/lobby, complete it, begin a mission and kick off the other one. Free-exploration is the closest to what you would get in a core PSO run, but there you're stuck in one zone with levels that are randomly-generated, feature respawning enemies, and even absence the set-pieces that made the zones in PSO feel as distinct areas. Therefore the end result is things tend to feel a whole lot more generic and samey within my eyes. but YMMV.
It is really the battle being so fluid that makes them range from tolerable to enjoyable. There is more I could talk, but I believe this gives you an overall idea. If you take Phantasy Star Online 2 on its own merits, it's fun. I feel it is no substitute for your PSO. And should you would like the gold-standard in waifu simulators, you've got your game.
I would've killed to get a PSO1/blue burst remake (or, hell, actually PSU), but at least the people who like Phantasy Star Online 2 will have the ability to play it without localization issues or having to confront the katakana captcha boss. One of my favorite things is how every single weapon type is different. My personality of choice was I think the robot hunter who had a high precision in order that they could viably use firearms alongside melee. Having something similar to 6 weapons felt awesome. Meanwhile PSO2 you jumped with one weapon and nothing ever felt to be an update. Phantasy Star Online 2 is rather fun, but it might also be a IP.
I have many fond memories of playing PSO Episode I & II together with my brother. At some stage we raked down the road in one of our neighbors and played with just about every day after school. They soon picked up their own copy, and after weeks of trying to find rare weapons, they arrived home one day and found that their younger sibling accidentally wiped their memory card. They moved soon after that and we've lost touch. Wherever they are, I hope they're just as excited for PSO2 as we are cheap Phantasy Star Online 2 Meseta.