Melinda, blogging at Stand to Reason, gives a good word about Halloween and Reformation Day:
Many Christians delve into the details of the history of Halloween in a sincere effort to try to make a good decision about what's pleasing to God; I just don't see the same time and attention given to studying the details of central Christian beliefs like the Trinity or justification, or the Apostles and Nicene Creed. I dare say that many of the Christians who decide they cannot participate in Halloween, have never taken note of the fact that October 31 is also Reformation Day - and none of us Protestants would be here enjoying the grace of God as we do if it weren't for that day. Even churches that decide to opt out of Halloween or opt in for Harvest Festivals take little notice of Reformation Day, which restored the Gospel message that we treasure.
... whether you decide to opt out of Halloween, which is just fine, or whether you dress up, let's also remember it's Reformation Day and that we have a treasure and privilege of studying the Bible ourselves and learning from the rich heritage of church history and the careful thinking and love for the truth people committed to hand down the faith to us. Let's be even more diligent in learning the full teaching God has revealed through His Word than we are in investigating Halloween.