The adventure game format is a great fit for Doctor Who, as are the stealth sections.
The short length might not be to some players' tastes, but it fits the story. I find it takes about two hours to play through an episode the first time, which puts it on par with most other adventure games.
The real-time re-creation of the show's title sequences are beautifully done, and it's overall a good demonstration of how to go about making a game based on a TV show.
That said, it does have a few flaws.
The characters are rather lacking in facial animation. The developers would do well to take a leaf out of Valve's book in that department. Their mouths sync up with the dialogue and they blink occasionally, but their faces are otherwise largely static, making the game seem a lot older than it really is.
The controls are a bit sluggish, though they are somewhat improved in Episode 5, due to it having been made later.
The music has a tendency to get a bit too loud when string-heavy action sequences are playing, resulting in the sound effects and speech getting masked a bit.
Finally, the sequences which are explicitly about solving puzzles (typically involving modifying some kind of device) tend to be much too easy, and even then the challenge is usually about actually going through with the solution, rather than figuring it out in the first place. I'm sure this was meant to give the youngest members of the audience a chance at solving them, but it would have been nice to have an option to make the puzzles harder for older players like myself.
Overall, though, it's a good game and it's worth dropping $10 on when it's on sale if you're a fan of Doctor Who.