Even though I'd agree Raising Cain and Bonfire of the Vanities are nowhere near De Palma at his best (Cain might have been on autopilot, but it contained moments no other director would ever have had the nerve to do, and Bonfires had that good opening long take following Bruce Willis and entourage through the bowels of the hotel), for me nothing compares to the complete mess of Mission To Mars. From garden party opening to going off with the aliens ending absolutely nothing rings true, and not in that 'heightened reality' way of the best De Palma (and Cain!), but in that 'crap script' way. At best everything feels cribbed from other films (Close Encounters, Apollo 13, The Abyss) and even from De Palma's own film in the scene where the astronaut is 'spun to death' by the twister that mirrors the far better handled (both funnier and sadder) similar scene from The Fury. The less said about how Skittles manage to save the day, the better! I don't think science fiction is De Palma's strength.
I also thought it contained Ennio Morricone's worst score, noodling away annoyingly in the background of the final alien scenes. De Palma seems to have had back luck in that sense as I really didn't like Bernard Herrmann's score for Sisters either. It felt that the films really needed scores of cold horror or quiet contemplation to counter the histrionics occuring on screen (such as Howard Shore's scores for Cronenberg that deliver that shock, but also a sort of feeling of numbness to the horror that is occuring), instead they ramp everything up to 11.
2000 was a pretty bad year, as I felt Verhoeven's Hollow Man completely missed the mark too, and both Mission To Mars and Hollow Man are still at the top of my 'worst films of the decade' list years later.
When you are up against Val Kilmer in Red Planet and his film wipes the floor with yours, your film is seriously bad!
EDIT: Maybe not 'worst films', as I'm sure there have been worse films made that I haven't seen. Perhaps a better term would be 'most disappointing' considering the talent involved. Strange how the invisible man story tripped up John Carpenter too. At least Verhoeven didn't turn the story into a comedy even if his film did devolve into a stalk-and-slash film at the end, albeit a spectacular one.