I've been having a good time with Retro Defense until the Long Distance level, where I basically cannot get past 6 or 7 waves (30 is the goal). I did move on a tad further and am also stuck on the Y level. But I'm really flummoxed by this one. Has anyone succeeded, and how'd they do it?
Here's someone's apt description of it, which mimics my experience:
I've figured out you have to use two small reds on the single squares in the middle of the level to start with. If you use one green or two greens you last until about level 5 or as soon as you get some yellows. Small blues don't work. You can get the slow-down turrets, but without turrets being in range at the back this is useless.
Assuming you have two level 10 small reds or a red and a green on the single squares, this will take you to about level 7 to 10 before they're overwhelmed.
The next obvious step is to get some big guns at the back. But, in order to get them in range before the level gets too high for the small turrets to handle, you will need to have been lucky enough to have collected three range boosting upgrades (or power+range combos) and have them in a row at the back all powering up a large red (I've never been that lucky), or you can use a large green (this fails at level 10 as it's too slow).
I've also tried getting large blues on the single squares at the bottom. I managed to get one once, but I died at level 9.