I think we all can agree on that Plazmaburst 2's gameplay gets very easily repetitive, because in my experience, atleast if we're talking about the Official PB2 campaign, It's mostly just shooting galery, there is no variency except that there are weapons that get more powerful and later enemies just simply become bullet sponges.
In my opinion, I think Plazmaburst 2.5 would greatly use of new elements in the game that will make it much more entertaining and provide a more dynamic gameplay, and I think we should firstly start with the Slow-Mo ability...
Slow-Mo Ability
Firstly, I think I want to address if how painfuly slow it is. Like I get the main idea for it is to slow down time, but in my opinion It's too slow; Not just your movement but also your weapons reloading, which makes it sometimes ineffective way to deal with enemies, especialy enemies that require you more powerful weapons.
In my suggestion, I think the Slow-Mo effect should be greatly toned down on the Player character, and slightly toned down on enemies to make it more fair.
Slow-Mo should make you gain immunity towards explosive projectiles (However not their explosion radius). And by immunity, I mean when you are under slow motion, projectiles such as Rockets or BNG's will fly though you without detonating, however it should not work for splash damage, you will still receive splash damage from Rockets or BNG detonated close-by to you.
In my opinion, it should make Slow-Mo much more useful, and certainly less pain in the butt to use in the process.
More Ability Ideas
Now, while we talked about the Slow-Mo ability and It's needed changes, I think it would also be great opportunity to talk about extra ability ideas for the Main protagonist in the campaign, and also perhaps make it available to use in Multiplayer competitive too.
Energy Shield Ability:
A pretty simple one, it should greatly reduce the damage you receive from enemy shots. In addition it should completely protect you from getting knocked out and sent flying from a powerful projectile hit. Using this ability should drain your energy overtime, and receiving damage shall speed up the process of energy drain. However receiving damage from deadly explosive weapons such as Rockets and BNG, it should be able to break the energy shield very quickly.
Stealth Mode Ability
Makes you invisible to the enemy eye, while in your screen your character become transperent slightly. I think the advantages of this ability are obvious. There are rules for this ability however; When you shoot you lose your stealth ability, however if you stop shooting your stealth ability returns, untill your energy has drained out. Under stealth mode you can commit stealth kills - If you engage in a melee combat, your character will grab the enemy character and then procced to make very deadly slashes on the enemy, dealing massive damage. Maximum 2 hits, If the enemy character has a lot of health, your Character will toss the enemy character after 2 deadly slashes.
Projectile Magnet Ability
Kind of like in the matrix - When using this ability (Which is Hold-button), you will generate energy field infront of you, stopping enemy projectiles from approaching your main Character. When you release the button, the energy shield will throw all projectiles (Bullets and Rockets) back at the enemies, however this ability does not work with Energy/Plasma weapons, so should be wary of that. Drains energy very quickly, so it should not be spammed and be overpowered in any kind of way.
Psi-Blades/Swords
I think this specific feature needs a little bit of overhauling. What I should suggest is, when you hold the 'Fire' button when you use the Psi-Blades, instead of slicing into the air, your character will hold the blades in defensive stance, consuming your energy as your character focuses. When you hold the button, your character will automaticaly deflect any incoming bullet projectile shots. When you are very close to an enemy character, you character will start slicing to damage the enemy character.