Well, I guess my spatial skills are better than I thought cuz after my failure on the first try, I did it quite on my subsequent tries.
Admitedly, the aiming system is quite confusing at times but usually it goes for where your aim is and/or the nearest target you're from.
It's a game that ask a lot from investments with the player to master it's mechanics. Also ... getting better parts from previous missions help a lot.
Though, I completly agree with the "no restart" part. It is quite the missing feature :/
But hey, I heard it was just a demo made with the E3 demo build so I guess the game is way further ahead in production and they probably changed lots of obvious things.
I managed to finish it. The boss got a lot easier once I realised I had a bazooka weapon I could equip instead of my stupid shield. I guess the aiming is something one could get used to, but I really want a restart option and the issue with big enemies getting close to the border still irks me. On my succesful try I got into a situation where the Colossal hit me so I flew passed the border, and all I could do was watch as the game took control and moved me right in front of the boss while it prepared another attack that once again pushed me beyond the border. Needless to say, it didn't make me happy.