If you think about it, a lot of great horror films have bad sequels just because the market demands you to make the other one right away.
Not all horror fans love Evil Dead because of the humor, at least not me.
I've seen a lot of movies that were great and scary, but not particularly fancy in their filmmaking or performance. And they're still scary, and I think a good horror movie should be scary above all things.
What some of the early horror genre masters knew, and what I know, is that the audience are perverts, but in the best possible way.
There are the horror fans that love the 'Evil Dead' because of the humor, but I'm sure it's not all of them. Not all horror fans love 'Evil Dead' because of the humor, at least not me.
I watched 'Evil Dead' when I was 12. I was going through all the horror I could grab. I remember going to the video store and asking for something 'real.' And the guy gave me the 'Evil Dead' VHS. When you're 12, you're not supposed to see that.