Fellow game dev here, and i played firefall PVP for 600+ hours or so.
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Movement doesn't feel as good as firefall.
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Telegraphing Movement: Firefall had boosters coming from your feet and that gave a better sensation of direction/control while the jets on your back feel vague and feel directionless. I immediately missed the jets on my feet and wished there were some more visible indications as to which way i was shifting my movement. Make sure how a player is moving and why a player is moving is easily telegraphed to a player. Here when you're hovering in midair it's kinda vague and vague feels bad.
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Skill Based Movement: From a PVP standpoint i wouldn't play any kind of PVP arena with movement like this. Not because it's bad, but it's just not suitable for players who enjoy skill based movement systems. There's a thousand games with movement that feels kinda weighty and floaty and unresponsive and this is too similar. But luckily this is pretty easy to fix with the systems you have in place.
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Movement 1: Emergent or Skill based Movement :
A good example is maybe I've discovered your first emergent-movement mechanic. Where you hit spacebar, then hit spacebar again and quickly hit shift and aim towards the ground. This results in a player more or less immediately transitioning from running to sliding, and sometimes this works really well and others its got no momentum at all. But it's fun to do and it's a natural kind of movement mechanic that immediately adds depth to how a player can move around the world.
Now if you try that yourself, and then imagine that every time you did it maybe your jets on your back gave you a boost. Suddenly you have a pretty cool form of movement that is skill based. But don't just make it an automatic thing, then its bad.
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Movement 2: Shift key should be boost:
The way i would embrace this is rethink what you've got hotkeys bound to and how you're using this jet engine strapped to a player's back.
You have shift, which makes a player run faster, and also uses your glider which isn't really a boost because your jetpack also has a boost with double tap. This is already confusing and really "Make player go faster" should be on the same key and "Put player in a new movement mode" should be on a separate key.
I would personally tie shift to firing your jets heavily backwards. Like spacebar but for forward movement. Make your character use fuel to sprint faster, allow you to use fuel to slide up hills instead of only down. Allow fuel use even in midair with spacebar to move faster in a direction you're strafing.
Then the emergent movement becomes jumping once, then shifting to boost and slide along the ground. This would be a lot of fun, a very unique form of movement (reminds me of vanquish which was really fun movement) and since you can't really shoot while sliding its a proper tactical choice.
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Movement 3: Your jetpack is simultaneously too powerful and too slow:
You had ... an embarrassingly large number of forum threads about jetpack speeds in firefall, and eventually jetpacks were made much faster, and given less fuel to compensate which made for a far better pvp experience.
I know your former Red5 devs know this and remember it well. But i will bring up something you may not have realized. Jetpacks+Glider systems being this strong completely trivialize your game design. Players simply don't have to give the slightest care in the world about the world you design for them, similar to the massively destructive impact flying mounts in WOW had on the playerbase.
I would recommend less fuel in general just so that your world design matters, and imo adding a boost button (players can use 2x or maybe 2.5x fuel to jetpack 2x faster) would make it feel less floaty and slow when you're trying to jetpack.
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Movement 4: The glider sucks:
I just press shift and i get a boost and fly in a direction infinitely with no player input and magical forward thrust? There's no player interaction and it's really boring to fly.
Remove the boost, remove the magical thrust. Then tie it to the previously mentioned boost key into allowing a player to use their own fuel to gain forward momentum with it.
Which immediately puts a logical understandable limitation on the glider and means you don't have to just jetpack upwards and then deploy it. You can use that fuel to move with it.
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Guns: Recoil:
Screen shake hurts my soul, that is all.
I suppose experienced players might also be a little frustrated that screen shake + recoil in opposite directions of one another makes it extremely difficult to compensate for recoil (i.e similar to counter strike). But i would ignore them completely.
You should really be designing the weapon recoil systems from the ground up to prevent hacking players. Hackers are such a massive negative influence in every game nowdays and anticheat is effectively useless if your recoil design is bad.
Your recoil patterns have a pretty consistent upwards trajectory per bullet (until later in the clip). Which means a simple c++ script can reduce the recoil a player experiences by 40-50%. Careful of designing too many weapons platforms like this, or you won't be able to control the cheaters and cheating will be required to compete (I.E Rust, or R6: Siege).
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I know the game development process well, and i know that sometimes just reading what someone else writes gives me great ideas to put into action. So hopefully this spurs some useful thoughts.