Ya.. I happen to be in the same boat with the rest who have posted here... That boat is, the can get past wave 23/24 boat . That is assuming you can even start at wave 19 and go to 25 to get the cheevo.
Because to be honest, even with only going from 19-25 is still way hard.
I've managed wave 24 multiple times...even with 2 or 3 lives, but alas i get raped...the ships on that level have a reflecting shield they put up every other second, which makes it almost impossible to do consistant damage with any gun.
My best advice so far is once you make it to 23...evade like crazy, shoot at opportune moments when you are at max distance and hopefully kill some enemies to charge up you Y button special. You should already have one Y special when you get to 23 if you haden't just used it. If you use your special on 23 and get enough kills, odds are you can regenerate the special almost instantly with the enemies you kill. This will effectivly give you two specials for 23. And with 24, all i have got so far is use your anaconda torpedo from far away....not quite sure but i believe its the most effective way to dispatch wave 24's enemies.
Also...if anyone else can confirm you can go for 19-25 to get the cheevo, I would greatly appreciate it.