The MCU: the character they could have used was...
The MCU has made some fun and successful films. All adaptations take liberties with the source, but the MCU seems especially prone to giving us in-name-only characters. Sometimes (Wong) that's for the better. Others, it's not, especially when Marvel has so deep a bench of characters that can serve the role Feige, et al. wanted for their scripts.
My case: Sam Rockwell gave us fantastic character in [I]Iron Man 2[/I], but it wasn't Justin Hammer. However, the film's character seems *very* well suited to the comics' Morgan Stark.
Others?