There are some very significant differences in this version. While it doesn't appear to be that fabled prototype free of slowdown, this version is playable to the end but is lacking some of the polish and balance found in the final version.
* One of the biggest changes in this version are the bullets that the droid unit fires. They're graphically different and fire a lot SLOWER than they do in the prototype version. Not a good thing as it makes it harder to destroy stuff.
* Default high scores are completely different for whatever reason. 1st place is 218,200 and 10th place is 48,500, whereas on the prototype 1st place is 196,600 and 10th place is 15,400, and yes the scores inbetween are different too. So it's easier to rank in but you still pretty much have to reach stage 5 just to beat the default high score, especially with other changes in the scoring and enemy layout.
* Extra lives are awarded at 20,000 and 60,000 by default, instead of 60,000 and 130,000. A little more forgiving to the average player, even if the first stage doesn't feel as easy (more on that later)
* Stage 1 - the first waves of enemies look completely different, and don't eject dudes into the air after you kill them. Booooo!
* Stage 1 - no points for destroying the cars on the ground, and there seem to be less of them.
* Stage 1 - the enemy formations that "materalize" into the screen are way different, and they take multiple shots to kill instead of one shot. The midboss tank appears way sooner while the materializing enemies are still showing up in waves, which is very irritating and actually caused a death on my first try because I didn't see one appearing near the bottom of the screen when I was trying to shoot the tank. This is very bad game balance for the first stage of the game so it's good that they toned it down in the final.
* First boss is pretty much the same but bosses in this prototype version do not have those "extra" enemies that come out from the right side of the screen and track where you are and generally take a lot of hits before dying. I theorize that these enemies were added to the final version to prevent people from camping in safe spots on bosses, as their appearances are time-based and since they take a lot of damage they force you to move around on the screen.
* Stage 2 - not as different as stage 1. The "generator" enemies produce fewer enemies and they're only worth 100 points a pop instead of 300. There is an extra set of human guys sitting in pods firing lasers before you reach the second half of the stage. Rest of the stage seems about the same, including the boss.
* Stage 3 - also not very different. The enemies that the ship at the beginning of the stage launches out take multiple shots to destroy instead of one shot. Not sure if the ship fires more homing missiles too? Felt like it but I could be wrong. Rest of the stage seems about the same, including the boss which is way easier when you don't have to worry about the "anti-camping" enemies.
* Stage 4 - some differences here. The enemies at the beginning that walk on the top and bottom of the screen seem to have less delay between their shots. The pods that open up and fire lasers to the left and right also have way less delay before they fire their lasers. The part halfway through that makes you dodge columns coming up from the ceiling and ground is harder - some of the columns come out WAY faster, and as a result it changes the timing on the safe spots if you're used to the final version. After that, the section with no environments to crash into that has enemies flying around that release little circular things that drop powerups, these enemies actually seem to die faster than in the final? A rare occurence of enemies that have less HP. The timing on the boss is slightly different before it opens up to reveal its weak points. And the weak points are colored yellow instead of green...?
* Stage 5 - first half of the level is pretty similar. The part where you go in the ship and the robots that "walk" in from the corridor might take a little bit of damage but I'm not 100% sure. When you reach the top-right point of the mothership, the turret firing bullets in an up-right direction fires them WAY faster which is a problem if you can't destroy it in time. Circling back around to the bottom part of the mothership, enemies released from generators again take multiple shots to destroy instead of one shot. The asteroid rush before reaching the last boss is WAAAAAAY THE FUCK HARDER HOLY SHIT. The asteroids fly out at nearly double speed AND take more damage. Fucking insane! I had to savescum this just to figure out how to get through this part without dying because you can't do the same pattern even when you're fully powered up. This part is some bullshit. After that, it feels like the lasers on the enemies right before the last boss move slower, but that may have been a rank thing from me dying on the asteroid rush lol. Last boss seems pretty much identical, no anti-camping enemies makes it easier, etc.
* Didn't notice any change in the ending text. Didn't play through the second loop so I'm not sure what changes there are in the second loop, or if the staff roll that appears after clearing the second loop is different.
