Buggy, but seeing as it's the first solid console title for US audiences, not bad fan-service.
Let's get the bad points out of the way first:
Considering the delayed release (originally scheduled for sometime in March) and not showing up until late May, I would have assumed it would have been a well-polished experience. My wife and I jumped eagerly into the two-player co-op immediately after downloading (the file is nearly 1500MB, by the way). I took on the Doctor, she as River Song. The split screen was nice, but some things were hard to see given the reduced size and overall darkness of River's opening level.
There were also several bugs right out of the gate. The Doctor began repeating dialogue as he passed certain points while solving puzzles. River had a few button response issues. These eventually cleared up, but the biggest and most obnoxious bug was when the two finally meet up half-way through the level. There was no dialogue between them or through the level until one of us was killed off and we had to restart from the checkpoint. It was only then that ALL of the dialogue that was missed began to play as if it was trying to catch up to where we were. Once it got finished though, it played fine for the rest of the mission. There were several other glitches along the way, but fortunately nothing that restarting the checkpoint wouldn't fix (however still annoying).
Switching over to single-player, I noticed the exact same glitch. There were also some issues with the AI-controlled River Song that included he standing around while the Doctor is waiting to hoist her up on a ledge. Or not defending the duo while the Doctor is trying to solve a puzzle. While the screen size on the single player game makes a world of difference, so does having a competent partner to back you up.
Now for all that is good:
The gameplay is very reminiscent of classic side-scrolling Prince Of Persia with running, jumping, climbing, pushing boxes, and crawling through tight spaces. The puzzles have 3 difficulty levels but even on hard, I haven't found anything that couldn't be solved within a couple of tries. My favorite so far has been matching frequency with the sonic screwdriver which is achieved by rotating the right analog stick with harder locks requiring the left stick as well. The platforming gameplay and puzzle styles have all been done before, but it's now got a shiny new Doctor Who wrapper that makes it so appealing for the fans.
Having only played through the first few chapters, I can't say if the story lives up to the series or how it ties in with canon, but so far it's very well voice-acted (just because you're a screen actor does NOT always mean you can voice act). The Doctor mumbles to himself and talks through problems while you look for puzzle solutions and River is as feisty as ever. When the two are together, they banter back and forth just like in the show.
There seems to be a good mix of villains from the revived series (though I personally have only encountered the Cybermen at the time of writing this) and hopefully they are all well represented. But what it all boils down to is this title is just fun. Racing the Cybermen through the underground tunnels and quickly using the Sonic Screwdriver to open doors to escape was just as exciting as watching the show...even if it did take me a few tries thanks to the AI partner not keeping up (we'll call that "replay value").
Final thoughts:
As a fan of the series, I'm very pleased with the way the story is shaping up. For $20, I'm happy with the value of the game. I do however hope there are updates that fix some of the bugs. While not system-crashing, they are still annoying and with the two-month delay, I would have thought those glitches would have been avoided. I highly recommend the game for hard-core Doctor Who fans and for people who enjoy a solid co-op platforming experience.