1. Spock - Star Trek III: The Search for Spock
The Death: In Star Trek II: The Wrath of Khan, Spock sacrifices himself to fix the Enterprise's warp drive, succumbing to radiation poisoning but saving the rest of the crew from Khan Noonien Singh (Ricardo Montalbán).
The Resurrection: In the sequel, The Search for Spock, Spock's "katra" (his living spirit) is returned to his body, though his memories are a bit of a mess to begin with. Still, happy endings for all.
Why He Should Have Stayed Dead: Much like the Agent Coulson death, it really
meant something when Spock died, as the friendship between Kirk and Spock had been forged over an entire TV series and two movies, meaning that the moment pictured above had a lot of emotional thrust behind it. That this was then turned around in the next movie completely undermined it. Though Spock's presence would have been sorely missed in all future Trek entries, perhaps don't opt for cheap emotions the first time if you're not going to follow through respectfully.
Which resurrected movie characters did you wish had stayed in the ground? Let us know in the comments below.