This film has courted some very negative reviews from people who feel that the film deviated too much from the original book and delivered something too coarse for a young audience. Those concerns are justified, and I would understand that a big fan of the book would feel that what they are seeing on screen is not reflective of the story they have enjoyed.
I do like the Dr Seuss book, but I'm not a die-hard fan - I do remember it from my younger days, but only the general gist of it rather than the full story. Maybe this is why my views on the film are less harsh than many others.
Mike Myers gives a very energetic performance of The Cat in The Hat and seems to understand the role well. There is a lot of over-acting which is required for the larger-than-life character, but he also captures the more understated nuances as well. Other than Alec Baldwin who is maybe a bit wooden (and I tend to think looks like he should be in pantomime) all the other roles are well performed and fit in nicely with the film.
The most impressive aspect of the film are the visuals. Although this is a live action film (which also makes use of CGI) it manages to look quite cartoony due to the incredibly vibrant blocks of colour. Because of the unique look of the film it seems to take place in its own universe, it creates a unique world in which you accept all the crazy happenings rather than looking plainly ridiculous. The book can be read in minutes whereas this film runs for nearly an hour and a half, therefore artistic license has been taken and it's probably best to think of this as a film inspired by the book rather a film of the book per se. There are some pretty funny moments in the film which are effectively comedy sketches woven into the plot - the best being a parody of a cheesy American infomercial for an automated muffin maker.
The dialogue in the film has caused minor controversy as many of the jokes are aimed at older viewers and some contain double-entendre. But the truth is that younger audiences will have no idea of this and it enables the film to appeal to audiences across a wider age range. My kids love this film and both myself and Mrs. DangermouseZilla have a laugh at it too, with the humour tending to be focussed at the more mature audience we can get something out of it too as the slapstick and bright colours aren't quite as appealing to us. Although it's more mature, the humour certainly isn't rude or smutty and we don't find it in any way offensive. I've read that some have taken exception to the phrase "I'll hurt you, and I'll make it look like a bloody accident" - but in the context of the film it's a line which is funny without any malice.
In a nutshell: Is this in the true spirit of the book? That's all down to interpretation and opinion. This could easily have been called something else and the Cat In the Hat could have been replaced with creature with a different name, but I don't get the impression that this is 'ripping off' the book. It seems to have been created by people who have revelled in developing an incredibly colourful film which is cheeky, imaginative, and above all else - fun. Surely those things are something close to the Dr Seuss spirit?
Is this film too mature for very young audiences? No - I'd rather have a family film which is slightly edgy rather than the over sentimental dross of Hannah Montana or High School Musical!