The Dirk Gently pilot was pretty great! It did a lovely job taking a few of the major strands of the first book and resolving them in the span of an hour, for a self-contained story in case there's no series. For starters, all the Doctor Who stuff is gone; no Professor Chronotis and no alien trying to prevent the destruction of his spacecraft. As such, Gordon Way's story goes a different direction (no Electric Monk either, [spoiler]though he gets a namedrop[/spoiler]); it's familiar and surprising all at once, which is a neat trick.
I liked the Hitchhiker's Guide movie, but I understand its flaws, too -- it seemed to want to keep the entire plot of the first book while adding new (and often not-very-good) scenes besides, and that came at the expense of, well, lots and lots of punchlines. The Dirk script is much smarter in determining what to keep and what to cut (though, again, the fact that a good chunk of the book was reused material from Doctor Who helped make that decision easier), and the result is a much tighter story that's still recognizable as Dirk Gently -- especially because a lot of the best dialogue is intact.
Stephen Mangan carries the show as Dirk; he nails the eccentricity and the roguishness and manages to walk the fine line where you can see he's taking advantage of his clients but he still does what's right in the end. When Susan accuses him of being a con man who exploits little old ladies, you want to defend him -- because damn it, he may have asked for a new refrigerator as an expense, but he DID find that cat and in fact finding the cat has been his primary motivation through the whole episode, no matter what other, seemingly more important things he's discovered along the way.
The rest of the cast is serviceable but not as memorable. Darren Boyd's Richard McDuff is frankly kind of a dick but probably more interesting than the version in the book. Susan's mostly there to play the role of skeptic, the little old lady puts in a good turn as another eccentric character, and Gordon Way's barely onscreen at all; the rest are just bit parts. Since the basic plot arc of the book is handled in this pilot, I'm curious as to whether we'll see Richard and Susan again or not; they have potential but I can't say I'll miss them if they don't come back.
All in all, highly recommended viewing, and I hope there's more where that came from.
Also, I want to go back and freeze-frame Dirk's big board, because it's got Easter eggs all over it.