I've taken a look at all of these and I'll go down the line and try to comment on each. I'll put some more time into them in the near future, just to see what it takes to beat each one.
In general, this is fantastic work. Some of these are just brilliant. There are a few places where I'd suggest tweaks, and a couple that I just flat-out don't like, but I'll try not to let my personal tastes get in the way. These levels are technically flawless, of course, so there are no complaints there. In some cases I think the solution is not obvious, and that's okay, except where more information is given in French than in English. Sorry, we can't have that.
I encourage everybody to try these levels and really discuss the details. MYM's first level set took several weeks to produce, and we traded dozens and dozens of emails in that time. Discussion definitely leads to better levels, so the more opinions expressed here, the better this work will turn out. Criticism helps, so say what you think.
01: Great level. Really fun, and somewhat easier than it initially looks. I think there's a little too much wood texture here. We should probably come up with some new texture themes soon. This level would benifit from a fresher look.
02: Another great one. A real technical challenge. I don't think the chrome texture works very well on big horizantal surfaces, as it was meant for detailed or finely tessalated geometry. Maybe another new texture would look good there.
03: Perfect. Do not touch. This level really took me by surprise. Strikingly original concept.
04: Cool idea. Well executed. Perfect.
05: Another surprise. Great idea. Hard. In many cases the poles block the view, but they look so cool reflected in the floor like that. Maybe it needs a change, maybe it's good.
06: I'm not a huge fan of racetrack levels, but I admit they're a nice alternative. If you're want to copy Kart's haunted house track you might as well throw in a castle model. Where did the wood texture come from? If you need or want textures, let me know, as I think visual consistency is a crucial part of a polished appearance for the game as a whole.
07: Good stuff. Fairly tough. Thematically fits with some of MYM's other work, which is important. I suggest no change.
08: I hate half-pipes. I'll refrain from commentary on this one.
09: Neat concept. Unfortunately I think the Neverball physics engine is not really capable of living up to it. I'm not sure what to say about this one, except that it's visually a bit bland and it's not challenging enough to deserve to sit along side most of the other levels in this set.
10: Brilliant. Fantastic. Perfect. Do not change.
11: Great great level. Perfect.
12: This one is tough. I like it a lot, but we should only allow one level like this to exist. Once you've spent this nickel you can't spend it again. Keep it as is.
13: I love this one. I wish that glass didn't have to be there, but I recognize that it's necessary. Good level.
14: This one is very much a MYM level. I get frustrated and annoyed by this type of stuff, but I'll accept it on the grounds that "rlk likes it" is not a necessary attribute for a level to have.
15: Another Kart race. Ok. I do kindof feel like complaining about the Thwomps. Crushers were the first item I added to the "do-not-do-this" list in the initial mapping documentation. It seems to work fairly well here, if you're willing to allow the ball to pass through the track. Great job on the shadow though. It's a subtle yet necessary effect.
16: This is another one that can't quite be fully served by the Neverball physics engine. The beginning is great. I spun the cone a few times and marveled at how smoothly and easily the ball came up off the bottom. That in-and-of itself is worthy of inclusion in SOME level. Can the number of lumps in the upper areas of the cones be increased? I'd just like it to be a bit less chaotic at the top.
17: Ugh. Playing this level I felt as though I had been utterly deprived of all control. I really feel the player must be solidly in control at all times. A level should test the players ability to control the ball, not the player's ability to ACQUIRE control of the ball. This level is long and complex, and I like that a lot, I just did not have any fun playing it.
18: Another MYM-esque pusher. That's cool, that's his style. Is the face on the glass really necessary? I found it popping in and out and conflicting with the near clipping plane, which was a bit distracting.
19: Great level. My only comment is: raise the goal coin count. Force the player down into those holes.
20: Nice. Tough. Generally very good. The blue texture does not look good on the poles. Maybe a vertical chrome OBJ rail would look nice there, all smooth and rounded. I'll model it if you like.
21: Not my kind of level. Technically fine. Keep as is.
22: This is odd. I didn't get it until I realized it's just a coin-grab. I suggest adding some of your blue blocks to this level in order to make the motion of the platform more obvious.
23: Overall this is a fine level, but is the column in the middle necessary? It's an anti-cheating measure? Is cheating really so bad?
24: I question whether 20 seconds is a reasonable cut-off. I recognize this is meant to be a very difficult time trial. I guess that's pretty good. Again, I like this style. This is the coolest racetrack level ever.
25: This I like. Very very difficult. Just an absolute test of skill. No flying, zooming, bouncing ball, just a slow, ponderous, steady-hand challenge. Perfect.