If you depend on candy and trick or treating to bring Christian joy, then that's kind of shallow. Scripture has a lot to say about Christian joy, and none of it has to do with physical trappings.
1Th 2:19 For what is our hope, or joy, or crown of rejoicing? Are not even ye in the presence of our Lord Jesus Christ at his coming?
3Jo 1:4 I have no greater joy than to hear that my children walk in truth.
Real Christianity is not "grim and humorless".
No,
but lots of 'Christians' are grim and humorless.
But, without them, we wouldn't have fun threads like these!!!