Did you enjoy the Halloween Update? I think everybody was expecting the two winners of the Art Pass Contest to be released for Halloween (all the more since Mann’s Manor very well lent itself to a season release), but of course Valve couldn’t resist and topped it off with some additional stuff and turned a simple update once more into an event.
At one hand I can’t help but love Valve for all this. Store and all that (which I intend to comment on soon) might be a controversial affair, but Valve always find new and interesting stuff to throw at us. There’s a lot of content and event given to us for free on a constant basis. We can surely argue if those new content is always useful and improving the game (or maybe just blowing up its complexity to ridiculous proportions), but show me another developer who provides so much new content in this scope and frequency for free [1].
The Horseless Headless Horseman is actually an inspired concept for an event map. If you take away the bells and whistles it really introduces an interesting new element which influences tactics and game flow. The HHH can easily create opportunities which a team can use to its advantage.
I don’t see the specific game mechanics of the HHH working on anything but an event map, but the basic idea of having a 3rd party NPC as interrupting element is not without appeal and could create some interesting variation.
Of course most of that new gameplay element provided by the HHH was very much overcast by the second big attraction of the Halloween event, the gifts. While the HHH could be integrated into the gameplay the gifts did actually nothing but to distract from it (to put it mildly). The moment a gift appeared everybody forgot about CPs and started squirreling around looking for that little box, lying around somewhere. Ah well, it’s for a limited time only, so have your fun while it lasts. And at least everybody who wants to avoid the spectacle can easily do so.
BTW Valve, well played that players could initially grab a gift while spectating. I guess none of the developers ever even had the idea to test for this. 
I wonder if the HHH will no longer appear as well, after the Halloween Event has wrapped up? Probably yes, but actually I would love to have that as a variation still available (e.g. per server setting).
Besides all that both new maps, Mann’s Manor and Mountain Lab, will have to prove how well they can be played. To be honest I have played Mountain Lab for only a few minutes so far, but since the layout is the same I expect it to play very much like Mann’s Manor. But I guess most players have done the same; Mountain Lab really drew the short straw by the event being placed on Mann’s Manor.
So far I’m under the impression that both maps are quite defense-friendly. But it will require some more sober gameplay before a final statement can be made.
RSS 2.0