We were there several years ago with our 6 year old and she got rather scared at times. She did enjoy the parade and trying to catch the beads and coins. There are lots of "body parts" lying around and chainsaw waving ghouls that seem to jump out from nowhere. The CM's do seem to recognize that the young ones may be frightened and often tone it down in their presence. It's foggy and very dark in some places. There seems to be an overabundance of teenagers running wild as the night progressed. It could be the fact that alcohol is served. The later the more "lively" the crowd got. If I had to do it again I would arrive just when the park reopens and leave just as it is getting dark. Most of the party-goers won't arrive until after dark. The lines for the rides are fairly short up until then.
Bottom line, I guess some 8 year olds would enjoy it and others would freak out. You know your childs level of fear better than any of us and can decide based on that.