EDIT: I've just released a new version of the mod. Among the changes are that the HP of the flier has been reduced to 60, and a melee attack will now always disable the jetpack of anyone it hits.
Well, I'd be damned, you actually did it, son. 
No, seriously I'm impressed, gliding physics work. You did great job on that. Flight still needs some tweaking.
I think you could get rid of ascending and descending (aka. jump and crouch) in favour of this set up:
- Right now, forward/backward acceleration works only in horizontal plane. Instead this commands could take vertical camera angle into consideration so you'll accelerate exactly in the direction you'd be looking at (though lift and gravitation still are applied)
- Right now, there is a lifting force that is somehow divided into one that is keeping alien from falling down and another one for rising (pressing and holding 'jump'). How about combining those two into into one passive force that can also be used for rising aka falling with negative speed? This also it leaves 'jump' command free and you don't even begin to understand how much I miss regular jump in flight mode
- Even right now ascending with 'crouch' command isn't that useful. Looking downwards works quite the same way, so why not make flight mode a default one as opposed to wallwalk mode, this way it will a lot easier to switch between the two in the heat of the battle.
In short, ascending and descending controlled by camera angle, speed and acceleration, while 'jump' is still used for jumping and 'crouch' used for toggling between modes (wall-walking mode and flight mode).
All in all the experience is still fun, haven't tried it in actual game though. Especially, with turning it feels right. Anyway I'm still here(could you believe that?), and I could do some animations etc., or just send you last .blend file. Great job so far my friend.
Thanks and good luck!
Thanks for your feedback.
Using vertical camera angle for lift control was actually one of my original ideas for flight. However, I found two problems with it. One, which would be relatively easy to fix, is that I want the flier to fly like an airplane, meaning it can't fly straight up. The bigger problem is that you would have trouble aiming the acid bombs, since you couldn't look up or down without having your lift change.
As for having regular jump in flight mode, the airplane analogy I've been trying to use doesn't allow vertical takeoffs. So, I set jumpMagnitude to 0 and added code to cause automatic takeoff if you're going fast enough.
I assume you mean descending with crouch, rather than ascending. Also, if you're going fast enough, looking down won't make you descend. You say you want flight mode to be the default. Do you mean when you evolve to the flier, you start in flight mode? I'm not sure how this would make it any easier to change between modes in battle.
If you could add a "tongue lash" animation (not my idea, I forget whose idea it was) as an attack, so it seems believable for it to have quite a long-distance and wide melee attack, I'd appreciate it.
