i haven't actually re-read this book recently but i remember it well enough to contribute some thoughts i think. being set in castle rock, it was nice to see a shout out to pretty much every other castle rock story that came before. dead zone, cujo, the body, shawshank redemption, dark half, even the sun dog gets some love. also a nice shout out at the end of the book to another four past midnight novella, the library policeman.
sympathy for ace? not so much. he was unapologetically bad. came out of shawshank, gets deep in the drug trade. does he realize his mistakes and own them? no, it's all alan pangborns fault for having the nerve to bust him committing a robbery. then he hooks up with a demon (or whatever leland gaunt is, it's not exactly defined) and shoots some folks and helps blow a whole town off the map. granted the good citizens of castle rock willingly jumped into gaunts craziness as well, but if ace had lived long enough for everyone to come out of it, i doubt he would have felt very chagrined about his role.
polly i don't think was super complicated. desperation at a prospect of a life of terrible pain made the magic trinket fairly appealing, many people would fall into that trap. she was intelligent enough to cast it off in the end at least. she was one of the few residents who willingly cast off gaunts tricks before his defeat rather than after. pride was another downfall for her, caring more about what the town might think of her than about telling her boyfriend the truth about her past, which contributed to the final chaos in some ways.
in many ways needful things seems even more relevant today. people seeing what they want to see. desperate to believe despite all signs to the contrary. sounds familiar huh? all of gaunts tricks had flaws that were easy to see through if you really wanted to. it remains an interesting look at human nature, how easy it really is to set people off, and just how willingly some people will cast themselves off the deep end over petty differences.
plus i'm a sucker for stories where everything goes full chaos at the end and whole towns/worlds fall apart. needful things, tommyknockers, phantoms (koontz i know but relevant), the stand even. as gaunt says, flip all the switches at once, sit back and watch the chaos.