Scanners. Though the "protagonist" wasn't that great a person either.
I don't think we have the same interpretation of that movie, and I've seen it a LOT of times...
Vale (the supposed good guy) sacrifices his body but he takes over Revok - Revok's eyes and voice change over to Vale's and there's a point in the sequence when Vale's face is melting off where you see him gain control. His solution is to overtake Revok. That's how I see it, anyway. I hadn't thought of it as an open ending but I suppose it could be viewed that way.
Re: THE THING, I'm sorta surprised there hasn't been a recent attempt to remake that movie. Hell, they're remaking every other movie from the 80s that was even remotely successful. I think the reason they haven't is because Carpenter's creature effects were so good that any CGI garbage they'd throw together nowadays would look like Sci-Fi Channel schlock. And it doesn't seem like there are any good effects people left in the business that actually make live action effects. It's cheaper and easier to do CGI so that's what everybody uses even though it looks pretty bad most of the time.
Re: THE DEVIL'S ADVOCATE, I don't see the Devil as actually winning at the end of that one. He just gets another shot at an antichrist grandson. Keanu could deny him again like the first time, we don't know.
Back to the topic, a few more off the top of my head:
DRACULA 2: THE ASCENSION (hey, it's been on a lot lately...)
KINGDOM OF THE SPIDERS (but they don't kill Shatner, goddammit!!!)
BASIC INSTINCT (open to interpretation I guess, but it seems pretty clear to me)
ROSEMARY'S BABY (evil baby!)
KOMODO VS COBRA (the melty-face guy comes back to life all lizardy at the end of the credits)
DR STRANGELOVE (the bomb, or maybe Slim Pickens being the bad guy)
I almost always root for the bad guys. It's more fun that way. :)