For a toddler or preschooler this is probably one of the best shows you can find! This has some serious quality and dedication put into every show and you can really see it. It's so cute that, although perfectly acceptable for the youngest set, I'd actually recommend it for older kids (and kids at heart) too!
Let me start with the animation. It is stunning! The detail is incredible, the colors vibrant, and there's an unbelievable amount of variation in scene sets. It would have been so easy for the animators to re-use a handful of scenes for each episode, but, except for the opening act, it felt like every adventure was in a new area. In addition to that, in the third season, you can see the animation has expanded to have more movement in the camera angles, panning and shifting the viewpoint through the episodes - it is truly a work of art. And, from a parental perspective, the transitions are slow (meaning you don't flick from a close-up to a distant view, to a different face, and back in the space of two seconds like so many modern shows do). This is better for a child's brain than rapid transitions which can train the brain to expect rapid-fire stimulation.
For season 1 & 2, each small episode (less than 15 minutes) has a problem to be solved and a solution to be found. As I write this review, there are 3 seasons available, and I want to note that the third season varied the formula somewhat - there might not be a problem that is 'figured out', it may just be a fun adventure. However, the overall focus is on taking a science concept and making it clear to a child. Things like: how does a spring work? Or, how do you make paper? Or what is camouflage? It's educational and a whole lot of unexpected fun! For adults, the solution may be obvious, but for young kids, the discovery may be amazing and the best part is the process of getting to that end point. The answer to the problem is not always discovered on the first try, but the characters keep trying until they figure it out! And sometimes something new and fun is discovered along the way that had nothing to do with the original problem! Science that feels like play!
So problem solving, science concepts, beautiful animation... with all that praise, why didn't the show get 10 stars from me? Well, it's perhaps a small insignificant detail to most people, but... there are so many made up words. For example, there is a pumpkin- like squash that shows up in a few episodes which is called a 'puffilump'. And many of the solutions to problems are completely unrealistic (like knitting a flight-suit to get something out of a tree). Since my little toddler sponge is absorbing so much about reality, I'm not a fan of too much 'unrealistic' in an otherwise educational show. Again, it's just my own personal preference and others might not find it irritating. Other than that quibble, it's a fantastic show and highly, highly recommended!