While trick-or-treating is something one can grow out of, the costume aspect of Halloween isn't. Had I the time and opportunity, I would love to get creative and dress up as something for Halloween. I was going to go to a Poe Masquerade Ball as No-Face, with a traditional Grim Reaper costume with the drama mask and probably find some kind of large hat so that the mask would be placed above my face instead of me seeing through it. (for me the creepiest part about him was the fact that his mouth seemed displaced)
Also, on the subject of Halloween as a religious holiday, it actually is the eve of All Saints Day. The adoption of the whole dressing-up-as-demons thing came on as part of some superstition that the demons were most dangerous at that time (I think, don't quote me), leading to a practice that is retained even where its religious roots are omitted much like Mardi Gras. (or where Christmas is headed)