Hi everyone, welcome to my convoluted mess which I am passing for as a guide. This is written using my PS Vita so any typos and Screenies not showing will be normal yay. Ti make a long story short, PS Nova is to PSO2 like how PS0 is to PSO and PSPo is to PSU. A Side story/Gaiden game to the main. It retains the freedom of character creation and most of it's combat style from PSO2. I'll try to elaborate on the important bits specifically assuming you haven't play and/or heard of PSO2.

Graphics and etc.
Due to the PS Vita's power not only is the Gfx, Sfx and other great but it includes other extras not seen in other games. That extra is that your MC is now actually part of dialouge scenes. Yes! F******g finally.

Gameplay
GUI
The menu selection is now below the screen, Enemy data doesn't show tbeir element but their elemental weakness. Just Counter is now shown in your character rather than the buttons.
Combat
It is similar to PSO2 with a few changes. PAs are now called GAs(Gran Arts) and PP is now GP. Earth element is replaced by wind.
All weapons are different compared to other PS Handheld games. Weapon palettez are rehashed and so are item pallette. Also the delay is extremelly short after a combo, heck you can just hold the attack button and your MC will continue to attack like a Madman/woman.
Chaining
Unlike it's predecessors chaining is very different here. Chains are no longer tied to an enemy but as a collective. What I mean is rather than say individually chained, all enemies on the screen are now part of a single chain. Tbis means thar when facing say 2 bosses at the same time, your chain from killing one of them still affects the other too. Another change that is major no mre cursing Noobs and AI for using GAs early, those doesn't consume the chain anymore and actually adds more to it. Reaching a high chain count activates Burst, it basically increases damage more, improves attack speed, lessens Techniques and GAs charge or wind-up times and some other stuff.
Exploration
Another difference is that your MC has a combat and sheathed modes. The former is where you run slowly and do battles while the latter allows fast running speed. This means no more sluggish movement when exploring stages/maps.

Don't post yet.