What do I mean by 'mechanical FS3?' It is a game which leaps the FreeSpace mechanics forward in the way you'd expect from a true sequel.
Up front, I'll say there's one area I think is a regression. Warships don't really interact with each other at all outside of scripted sequences. Those sequences are spectacular, but they're not mechanical. It's pretty cool that you get to shoot the beams on the game's equivalent of the Lucifer but it's not really gameplay.
In FreeSpace 2, your fighter moves forward, turns, and boosts. Your speed is set by a granular throttle. Your turn rate isn't tied to your speed, so the effectively fastest way to turn is at zero speed (turret mode). The core tension in the game is between the need to point your nose at the enemy to attack and the need to turn away to defend.
In Call of Duty: Infinite Warfare (IW henceforth), your Jackal can swap between atmospheric-style forward flight and 6DOF mode, like a helicopter or a BSG Viper. This is done with really excellent simplicity — there's no glide toggle, no mode switch. If you're pressing the forward button (W), you're in classic flight. If you're not, you're in 6DOF mode. It's completely natural.
Defending yourself against an attack from behind is, like in BSG, just a matter of letting off the throttle, flipping around, acquiring the ship shooting at you, and side-thrusting/reverse-thrusting while counterattacking. But this isn't risk free: your attacker already has you acquired, and gets a pretty good chance to kill you as you stop accelerating away, flip around, and search for them.
More importantly, this totally mixes up one of the core parts of FS2: making attack runs on capships! I'll defend the bomb run as a Fine mechanic, all in all. It's cool to line up on your target and burn in, trying to get a lock while under flak and beam fire. But the process of resetting — getting distance again, turning around, reacquiring — can get pretty old when you have to do it again and again. Twenty years later, I'm thoroughly sick of it. In IW, you sidestrafe around your target like an attack helicopter, dueling with its turrets and spewing out countermeasures while it tries to kill you back. You're always looking at the target, always aware of what it's doing.
In general IW is much faster and more aggressive than FS2. There's a checkpoint system, which makes it less annoying that you both kill fast and die fast. I don't think that a faster pace is strictly better than a slower one (notably, many attempts to make FS2 'faster' by cranking up velocities and distances actually create a slower experience than the core game's in-your-face Tempest spam), but it's an interesting change.
Missiles in IW are extremely deadly, and capships in particular like to spam them at you (which adds to their credibility as something more than props). Your countermeasures actually seek out and intercept the incoming missiles, which is very cool.
FreeSpace 2 has an infamously huge number of targeting controls. IW has one: focus on the target in your reticle. This gives you, as far as I can tell, a little bit of follow and autoaim.
IW also has no radar. The radar is in the game world: all enemies are marked with icons which tell you their type.
What I like about this targeting change is that you spend no time at all staring at the little box in the bottom left of your HUD while fiddling through targets. What I don't like is that I can't quickly target my attacker, but the game, usually, gives you an arrow to help point them out. IW has no escort or intercept tasks, which is a shame (there's a reason I say a mechanical sequel), so it's hard to know if the 'use your eyes' targeting would fare well there. I think it would. Giving bombers distinct icons would probably work fine; that's more than Ace Combat does and it's generally not hard to locate bombers in those games.
Subsystem targeting in particular is just miles ahead of FS2. No, you can't cycle through subsystems without looking at the target. But the models are detailed enough to make it plain what everything is: just look at what you need to kill and press right mouse/left trigger. (An advantage IW has here is that you are faster and more agile than in FS2, which makes it easier to travel around a ship and find the turret/subsystem you want to kill).
I can't tell you how enormously more accessible this makes the game, without actually costing it any depth. It strips away an entire layer of abstraction. You no longer need to learn how to use the radar and targeting box at all. You instead need to learn the skills the game requires of you anyway - navigating the world and looking at it.
Health and Ammo
IW has a truly excellent support ship (really just an animation, I suspect, rather than a simulated ship in the 3D space) which flies up in front of you and docks to your prow to slip you more missiles. You also have regenerating health. I don't know if I like this more than FS2's regenerating shields, but it's fine. It's fine.
All you'll fight in IW's space combat are enemy fighters (Skelters) with regular or ace pilots, enemy gunships (A-JAKS, whatever that mean), and enemy warships ranging from destroyers to full-on carriers. The Skelters are fine enemies; they're small, nimble, and incredibly aggressive with their use of 6DOF flight. They die satisfyingly quickly if you can catch them, especially if you nail them with a heavy anti-warship weapon.
The larger warships are the real stars. They have lovingly detailed arsenals, with at least three different kinds of anti-fighter gun and VLS silos which seem to fire at least two different kinds of warhead. In combat they're constantly barfing dakka and missiles in all directions; someone at Infinity Ward really enjoyed modeling all the little guns and making them work! They really seem like lively, intelligent foes which want to survive and win. My only complaint is that they don't maneuver much, and you'll never, afaict, see them roll or pitch to protect themselves. You'll kill a lot of smaller warships, but carrier death is reserved for major plot points.
If IW were a full-on space shooter I'd wish for many more enemy types. Alas, it's not.
You get six possible primaries, three for the antifighter slot and three for the anti-capship role (though both can cross over in a pinch). They're all great, as you'd expect from Call of Duty weapons. I particularly love that some of the heavier cannons will propel your ship backwards. All of them are much more tactile than FS2's guns, with viewshake and tons of particle effects, but you'd expect that from 20 years of progress. Of real note is the excellent sound design.
Star Citizen bull****
Look, I wouldn't want this in an FS3 sequel, but I'll point out it's there. This game doesn't just have 'FPS levels' and 'space levels'. You will, at scripted points, transition seamlessly between your fighter's cockpit, to the hull of an enemy warship, to the interior compartments, and back to your fighter. You'll blast from planet surfaces up into orbit without load screens or mission breaks. The illusion is seamless. It's all scripted, but it looks amazing. Most of the game by playtime is on foot FPS-only levels, but the space levels are what I'm concerned with in this review, and they're not 'just' space levels, they're space-and-shooter interplay. The FPS space mechanics also give you full 6DOF control, as well as a grappling hook, mag boots, and self-steering thruster grenades.
To me, the flight dynamics and targeting changes are the biggest claims IW makes to being a true mechanical generation 'past' FS2. It has some genuinely good space shooter design. If you ever see the game on discount, I strongly recommend it. It's a great campaign, tepid villains aside, and a wonderful look at what could've been if space shooters kept rolling.