It's not acting that is bad - it's the casting!
Out of all the characters in the book, in my opinion, there were only 2 actors who fit the characters:
Gary Siniese - I would never have thought of him, but he was perfect
Bill Fagerbaake - I thought of him as I was reading the book back then. I'm glad they picked him
I thought no one else fit the characters as described in the book. Molly Ringwold was too old. Fran was supposed to be 21. Corin Nemec was way too thin (should have been someone like Phyllip Seymour Hoffman). Matt Frewer was all wrong for the Trashcan Man - should have been someone heavier - another Phillip Seymour Hoffman type. I always thought that if Trash hadn't had such an abysmal childhood, he would have been a fairly insightful, intelligent person. They played him like a complete nutjob. I didn't get that from him in the book. Jamey Sheridan was all wrong as Flagg. He doesn't have a menacing bone in his body. I didn't find his interpretation of Flagg the least bit scary, and he should have been.
That's just my 2 cents.
"Well, make something up!" (RG)