Wherein we slay a colossal space-worm, then face a not-so-shocking plot twist, then move on to the rather off-puttingly simplistic final battle.
A quick rundown of all the PSI powers and how they factored into my play style (or failed to).
Like I said, the Psycho-Reflective Screen power is complete junk. 15% damage resistance isn't nearly enough to make a significant difference, especially on Hard and Impossible. That's why when I did my little restart I went with Psychogenic Cyber-Affinity instead.
The +2 Psi boost is doubtlessly the best of the second year choices. Endurance doesn't make much difference at all on Hard mode (a whole 3 HP!) and Research is available for free once you get the respective implant (which is on the very same floor as the only item in the game you NEED to research to proceed...). Might as well get all the mileage you can out of your powers if you're playing OSA, right?
I haven't changed my stance on the third year choice, though - Psychogenic Agility is the only one worth picking there. Electron Tampering and Reflex Dampening are both completely worthless.
Kinetic Redirection - I didn't take it, but honestly, looking at all of the numerous items that are out of reach by any means other than this spell, it's not too bad if you take it as one of your starting freebies. Not as good as Psychogenic Agility or Psychogenic Cyber-Affinity, certainly, but not a bad choice.
Psychogenic Agility - A power I really should have used more. Extra speed to avoid attacks and falling damage is a good thing.
Psychogenic Cyber-Affinity - One of the most useful powers in the game, no doubt. Lets you hack with the best of them up until the endgame (and with 2 Cyber and a Tech implant, it's just enough to sneak through the final battle too).
Projected Cryokinesis - Sad to say if you're going for a pure Psi approach, this is the only power that does any damage to machines. As I took a bit from all of the three branches, though, this was mainly just reserved for when I was desperately low on ammo.
Adrenaline Overproduction - A good power to have in a pinch, as it adds a massive punch to your melee attacks. Hell, pair that up with a Psi weapon, the Smasher OS upgrade and a decent Psi score and you can one-shot Rumblers. I didn't end up using it all that much, though.
Cerebro-Stimulated Regeneration - Used it too many times to even count. 10-12 HP for 2 Psi points is a great tradeoff, especially given that it heals instantaneously while hypos, medkits and worm chunks take a few seconds. Easily one of the best powers in the game.
Localized Pyrokinesis - I didn't use this one, but it can prove to be fun on lower difficulties. Cast this spell, cast Invisibility, then watch everything around you die. Unfortunately the damage it deals isn't significant enough to be worth it on Hard and Impossible.
Molecular Duplication - This one can be a lifesaver when you're running low on ammo. Just be careful not to run out of Nanites like I did...
Electron Cascade - Hands down, a must-have for a Psi user. Keeps your implants and (more importantly) your powered armor charged. Even moreso if you choose to pursue the Energy Weapons tree...
Projected Pyrokinesis - A very powerful ability to have against biological targets, where it can even take out Rumblers with only three or four shots. Worthless against robots though.
Psionic Hypogenesis - I think I only ever used this once or twice to sneak past a Rumbler. Honestly, I'd say go for Invisibility instead - one casting of that will enable you to bypass multiple enemies instead of just one, so it's far more efficient points-wise.
Photonic Redirection - Well, you saw firsthand how handy this was in the last two entries. Lets you skip out entirely on some battles that would otherwise be downright grueling - multiple turrets, several security drones, a large group of Reavers and Rumblers, the four-spider trap on Deck 4... all neatly bypassed. Better yet, not having to destroy enemies means fewer surprise attacks from randomly spawned ones later on.
Electron Suppression - I didn't take this one, but it sounds significantly more useful for a pure Psi user than Psionic Hypogenesis. Not only does it stun a robot for several seconds, but damaging them will not cause them to snap out of it and attack you. You're still probably better off avoiding them entirely with Photonic Regeneration, but in the rare instances where you need to destroy mechanical enemies (like the Cyborg Assassins on deck 4), this could come in handy.
Molecular Transmutation - Another one I didn't take (largely because the Recycler does its job quite well), but apparently you can get quite a few more Nanites out of this power with a high Psi stat. Recycling stuff like grenades, prisms and worm beakers yields much higher payouts with this power. Might be worth looking into if you're not going to take the Hack skill...
Cerebro-Energetic Extension - Another one I didn't end up using a whole lot. Still, pair it up with Adrenaline Overproduction and you can carve through Rumblers like they're nothing.
Remote Circuitry Manipulation - This is basically the Psi equivalent of the Hack skill, only using half of your Psi stat as your Cyber and Psi points instead of Nanites. Not that good, but it does have some interesting uses as it operates at range. Like hacking Turrets while out of their range...
Advanced Cerebro-Stimulated Regeneration - Not a very good upgrade from the Tier 2 version. You can generally top of your health and save yourself a point by casting the tier 2 version twice....
Soma Transference - This one's a real killer, as we saw. Instantaneously drains a chunk of HP from any non-robotic target and adds it to yours. Unlike other attacks, it can also pass through Metacreative barriers (including the one surrounding the brain of the Many), so you can just put up a barrier in front of a Rumbler or a Reaver and drain it to death while it desperately tries to get to you.
Metacreative Barrier - For when you want to shut out distractions while doing some precarious task, like hacking a console, healing yourself or dividing up large groups of enemies; especially handy for the last two battles. Also goes well with Soma Transference, as stated.
Psycho-Reflective Aura - Another one I didn't end up using much. It may just be the mentality by which I approach this game, though - with all the powers you have at your disposal, it's easier to just avoid damage completely...