My stars! Some of the weapons are really, really, hidden in this game. I just found the quantom variegator weapon i.e., purple heat-seeking shot and I'm not sure if I would have ever figured it out if I hadn't been reading through this thread and come across a hint.
I also saw a hint in this thread about how scanlines are an indicator of an entrance to the secret world areas. I had already found one of these on my own but with this clue I was able to find a second one. Hooray! But even knowing this tipoff it still took several minutes of trial and error to find the exact spot where the entrance was. I don't know how you'd ever find this without that hint except by sheer dumb luck.
Still, I've enjoyed the heck out of Axiom Verge. I have nitpicks with the game but they're only things I care about because I've enjoyed it so much.
edit: I know I've seen the tipoff scanline effects in other areas of the game. But it was before I know it was a hint on where to find the secret world access points. Now I have to hunt for those all over again. Drat!