(In no particular order)
Kirsten Dunst as Mary Jane Watson
I thought she was great in the first Spider-Man film, but her performance seemed to lack more and more with each film. Plus, I wish she brought more of the sassy kind of MJ that was in the comics.
Val Kilmer as Batman
I honestly think that the Batman Forever suit looked cooler and more ripped than Michael Keaton's suit, and Kilmer looks more like a Bruce Wayne than Keaton IMO. But Kilmer pretty much sucked in the suit.
Michael Chiklis as the Thing
I believe they got the overall design right for the most part (except they made him look kinda small compared to how I would've liked him to be), but the overall delivery was sort of mediocre, IMO.
Halle Berry as Storm
Again, the design/looks were on the money but for some reason, I think Berry could've done much better.
Megan Fox as Mikaela Banes
I know that a lot of people don't like Fox's acting (for good reason). I think she's hot, and probably somewhere in my top 10-15 celeb crushes, but her acting isn't really the best.
Jim Carrey as the Riddler
I honestly find it difficult to take Carrey's version seriously.
Brandon Routh as Superman
Now I know that at least 98% of people I know say that Routh's take on the Man of Steel was craptastic at best, but I sort of beg to differ. He does get the look almost perfectly, and he could have done much better if he had a better script to work on, but his overall execution wasn't the best they could've done.
Jack Nicholson as the Joker
I like/appreciate how Nicholson's take was quite close to the comics' version, but he was too recognizable and too comical to take seriously. Heath Ledger's take was FAR better, IMO.
James Marsden as Cyclops
Yet again, another looks-on-the-money performance, but Marsden's take on the character was decent at best.
Tyler Manes as Sabretooth
I'm surprised I didn't put this on my worst of list. Manes' take on the character was incredibly unintelligent. Liev Schreiber's version was much, much better.
Uma Thurman as Poison Ivy
Had she received a decent script, she would've been cool as Poison Ivy. But it was just yet another Joel Schumacher screw up.
Well, that's my (short) list. My next in the series will be on upcoming CBM performances I'm stoked to check out.