I've so far just glanced at the stages. Here's my progress (times denote time spent on puzzle, a * before the puzzle's number means I've yet to complete it)
1: 0:07
2: 0:31
3: 0:08
4: 0:22
5: 0:18
*6: 2:41
7: 0:11 -- with one fewer move than given
8: 0:33
9: 0:32
10: 0:14
11: 0:41
12: 0:13
*13: 1:42
14: 0:17
15: 0:22
16: 0:21
17: 0:36
*18: 1:35
19: 0:49
20: 0:25
21: 0:48
22: 0:13
23: 0:33
24: 0:28
25: 0:14
*26: 2:50
*27: 2:00
*28: 1:40
29: 2:04
30: 0:30
31: 1:02
32: 0:12
33: 0:52
34: 0:28
35: 0:34
*36: 2:00
*37: 2:12
*38: 2:30
*39: 3:13
*40: 4:35
I just glanced through them thus far -- I'll probably look at 36-40 a lot better when I have more time. I got #32 practically immediately because of the way I approach the puzzles. My mind first looks for colors of panels that only have 3, 4, or 5 of a color. 32 has two sets of threes, so my first impulse is to rid myself of those, first. It just so happens that my impulse was correct.
This is also why 27 and 28 have given me problems so far.
Also, regarding #22, I think that there's a stage in the SNES Tetris Attack's puzzle mode that is VERY similar. I think it's 5-3 or 5-4, forgot which. I know I recognised that pattern from somewhere.
I also tend to have a hard time with "tall column" stages, like #6.
So... 29/40 solved on my first glances. Although 36-40 weren't passed immedately... can't say which is my favorite yet because I have a feeling that one of those I've yet to pass is going to be my favorite.
Overall, though, a very nicely-made set of puzzles. I mean, the solutions have been clever -- these puzzles remind me a LOT of the later stages of SNES Tetris Attack's puzzle mode. Just, in design and in how the solutions are obscured. I'll take a better look at the later puzzles sometime.
Only minor gripe is that I'm not a fan of the "start with 3 or more of a color in a row" puzzles (30). Personal preference, that's all.