I used Skywind's tips and I won hard badge relatively easy. Most of my survival scores was about 30-50 kills, then 120, 150, 213 and 319. As you see good start is most important - you need some luck to get nice weapons etc. After you rack up about 100 kills you can just stand next to the wall and shoot gauss gun constantly. Recede from the wall only for lives and time stops. Pick the ammo up only at stopped time. Check out Skywind's tactic.
I totally agree with CrystalShadow. Using this hintbox you can solve every puzzle as mindlessly as easy sudoku without even thinking what's going on and what operations you're doing.
I found grenades extremely useful. I bought minigun directly after fully upgraded SPAS thanks to 3 grenadies per wave. When I got minigun before wave 40, and then game was fairly easy, so basically I recommend this way :)
Really good game. Pleasuring for the eye, relaxing because of the music and very clever because of the challenging puzzles. I'm looking forward for Revert to Growth 3.
Yeah beating it in one day is insane, but it would take at least half an hoour without any upgrades, so it isn't really fast beat :P I beat it in 7 days (I hadn't cash for all upgrades unfortunately). With no stupid failures it can be done in 4-5 days, without spending years shooting the last boss of course.
Very nice concept indeed, but moves of the black titles should be limited. Otherwise the 15 of these levels can be solved almost by moving the black squares only, what isn't very creative.