I know the thread called for "good movies" that were ruined by director's cuts, but even though it's a horrible movie in its theatrical form, it's important to emphasize just how wildly miserable the director's cut of Rob Zombie's Halloween is.
TW: Sexual Assault
In the theatrical cut, Michael breaks out of the sanitarium during a cell transfer. Fine, efficient, whatever.
The director's cut has a redneck orderly and his redneck cousin break into the cell of a new mentally ill patient, drag her into Michael's cell, violently rape her, force Michael to smell their fingers after they forcibly penetrate her and then Michael kills the orderlies to escape. The only fucking reason this happens is because Rob Zombie is a talentless shock jockey hack that can't write a single fucking project without loading it with sexual violence.
In addition to this change, the cut is also loaded with even more of that trademark Zombie dialogue ("[eggs] are chicken abortions." "They're not chicken abortions!" "Yeah, like you know what an abortion is."), the death scene of the already-nude Lynda is only changed to include a wider shot that shows her genitals, and there's a few timing changes and added shots of gore.
This director's cut is the only cut available for sale physically in North America and has been since release. Zombie allegedly pushed to make the theatrical cut as inaccessible as possible, preferring his director's cut instead. If you want the theatrical cut, you can buy it digitally on certain storefronts or you need to order a Blu-Ray from Canada that works in NA which is what I did to complete my Halloween collection. The same goes for the director's cut of Zombie's Halloween II, though that's it's own can of worms and is borderline a completely different, far more sinister and nihilistic film than the theatrical cut.
No matter which cut you watch, they're utterly terrible and Zombie is absolutely bereft of writing talent, but the director's cut of that 2007 film just always stands out to me for being so fucking vile for absolutely no other than reason than Zombie seems to get off on that kind of shit.