Actually it has taken quite a while until Halloween 'arrived' in Germany. I don't mean until it was the 31st of October, naturally, but until people started celebrating Halloween like it's done in the United States.
Classically, we Germans wear costumes on what we call "Fasching". This is celebrated about 40 days before Eastern, usually around the middle of February. Originally "Fasching" (also called "Fasnacht" and various other names) was the last time people could really dig in before the feast leading to Eastern began. As this time also roughly is the end of winter and people always liked to 'drive the winter out,' "Fasching" was celebrated originally by putting on some horrible disguise and scare the demons of winter into leaving.
During the time, in certain areas of Germany (including the one I live in) people started celebrating by putting on less horrible and more amusing disguises and drinking a lot of alcohol - before the church would forbid it.
Now we fast forward to the end of the Nineties. As so many other things from the English-speaking countries, Halloween came to Germany for the first time. In pubs found in various German town there was a Halloween party. Some people started renting out old castle ruins and the like to celebrate there, dressing up as monsters and scaring people just passing by. Slowly the shops caught on, selling suitable costumes in the weeks before the 31st. And, as the 1st of November is a holiday everywhere in Germany, people took to it quickly. They could celebrate all they liked, as they would always have the chance of sleeping in the next day and nursing their hangover.
Finally, the children got the hang of it, too, and there are even some walking around and playing "trick or treat" on the 31st, even though it's not a major thing (especially as they get the chance to walk around the neighbourhood with a hand-made lantern on the 11th of November anyway).
I personally, liking everything spooky, the colour orange and the October (because I was born in October, too, see "Happy Birthday for me"), love Halloween - for the many scary movies and reruns of "The Simpson" Halloween specials on TV.