I am having a nostalgic day and logged into Newground's to watch some Flash. You have clearly stated you are not making a continuation and are not very active on the flash scene. With that understanding I did see noteworthy aspects to apply in new projects if you want to get back into it.
Positives
+Menu: Good music, sound effects, and organization. The scene selection was helpful and I liked the quaint alliteration of titles such as 'Lethargic Laboratory'.
+Intro: On point and easily my favorite part ('Interplanetary Indoctrination'). The 3rd person perspective of different video game characters on their respective worlds watching the test subject fly through space in the blue beam was incredible. Loved the upbeat Asian music and how it changes in the song were synced with changes in the animation. The looping animation of the blue beam background inside the beam was cool. At the end you joked about not having credits. You didn't need them because you already nailed it here.
+Camera work: Very cinematic. Dramatic angles. Utilizing the foreground, middle, and background. You even had decent faux 3D. EX: When Marichu wakes up in the grassy field.
+ Animation: Loops such as the computer screens in the lab or grass blades moving in the wind made the world feel alive. Rain on the window of May's car with wipers a cool effect.
+ Sound work: Loved the little touches. Like the music on the radio in May's car. You could still hear it slightly muffled after she opens the door and steps out.
Negatives
The entire video comes off like an art project where you are just testing animation techniques and have no coherent story or character's.
-Pacing: Too long for the attention span of the average Flash movie viewer. Very slow and boring after the lab and intro. Many things could have been cut down without sacrificing the artistic message and you would have increased viewer retention. Forgetful Fields and Sanity Scrap Yard are the biggest offenders. You joke about the length in the description and at the end even have a joke argument with the other writer about the ridiculousness of the junkyard fight scene. It's not a joke. Take your own advice.
-Voice Acting: Male voice acting was bad both in delivery and audio quality. Kira is a pro and as expected did okay as May, but even she sounded uninspired and unsure of what you were going for. Create more interesting characters and explain their objectives to your voice actors. The rest will come through naturally.