CC1 (4/5): Still my favorite. The design quality is top-notch, with some levels based on concepts that would normally be considered uninteresting or flat made much better by aesthetically pleasing design choices (such as many of the ice mazes). It also has the best difficulty curve of the three sets, though it misses an opportunity to provide a few true capstone challenges in its final stages. A few of the levels can be quite artificially difficult due to length, but most of them still manage to hit the mark and provide an interesting change of pace.
CCLP2 (3/5): It's hard for me to judge this set because it's the first (released) sequel to the game, and as such, it will always hold a special place in my heart. I don't think a small pool of levels bode well for quality design, but the designers featured most prominently - Eric Schmidt and Tyrethali Ansrath - showcased some truly stellar entries. CCLP2 also seemed to represent the collective shift in design tactics away from the one-note designs featured in the original game to levels that incorporated several concepts, clever applications of certain tiles, and new and inventive tile combinations that were not feasible in the original game. Some of these worked, while others did not, but for the most part, CCLP2 provided what its audience hoped to see: a new set to play that was fresh and different.
CCLP3 (4/5): It's especially hard for me to judge this set because I spearheaded its production, and as such, my opinion is probably not the most objective. But I can say that I don't believe it to be perfect in any way. The level design is probably the best among the three official sets, mainly due to the larger pool of levels and a longer submission period that allowed designers to become more seasoned. And yet, these two factors also proved to be the set's curse. It's pretty evident that the levels favored the most in this set's voting were the many that were the most well-designed, clever, or optimization-friendly, which typically translated into a large amount of difficult puzzles. The good news is that for the patient player who is willing to spread out the journey through CCLP3 across a long period of time, these levels and their challenges are fair for the most part. The somewhat bad news is that CCLP3 arrived almost exactly at the turning point when the community began to experience a major paradigm shift from optimization-centric playing to casual playing, the merits of both of which I can completely understand. But this set is definitely not for those who seek instant gratification.