Well, the adventure games tell reasonably Doctor Who-ish stories. Various game mechanics tend to repeat quite a bit, like the puzzles, or sneaking through areas guarded by enemies, which doesn't really happen all that much on the actual TV show.
The first four episodes were comparatively short, and very linear. Sometimes you play as the Doctor, sometimes you play as Amy, but the character you're not playing is either standing around somewhere or following you, so it's still very linear.
The gunpowder plot is considerably longer. They've added Rory into the mix, and they made the switches between characters more meaningful as characters might split up to do different things. It's still linear progression, and switches between characters happen when the game says so. As for the game itself, it's still the same: Doctor Who-ish enough to be enjoyable, but more repetitive than the TV show would suggest.
It's not the must-have AAAAAAAAAAAA game of the millennium, but it's certainly a game to consider for a Doctor Who fan. You might want to pick it up on a sale, though.
Controls aren't the greatest achievement either, but it's not an action game of any sort so there's no actual issue with that.
Hint: try to search the areas carefully if you want to complete achievements. For example, if you're missing a "card" from the first four episodes, there is no hint where that card might be, so you have to replay all of them (at least until you find the missing cards). For "facts" you do at least know the episode where you have to search, although you still don't know which of the three acts you should be searching.
The Gunpowder plot, being considerably longer, gives no hints where a "fact" might be missing, and it has no way to start somewhere in the middle. So, take your time to search every spot for "facts" on your first playthrough.