The title says it all really. I wasn't familiar with the franchise at all, but apparently the Clifford stories have been going strong for a good 50 years. It's an unflinching kids film, the kind that doesn't even try to appeal to moms and dads, then again kids are the film's primary target audience.
Emily feels like an outcast. She doesn't fit in with the kids at school and her home situation isn't exactly stable either. Her life changes when she finds a little red dog who changes overnight in the biggest dog the world has ever seen. Emily is finally happy, but others want the dog for monetary gain.
Whitehall's American accent is a bit disappointing (and unnecessary), the CG could've been better and the message of the film is really cheesy, but there's some British charm that makes you wonder how much better the film would've been if it had been set in London. Nice if you have kids, borderline if you don't.