Highlander....awesome concept, awesome potential....completely ruined by idiotic decisions and idiotic people in the position to MAKE those decisions. The series was as good as it got once it hit its stride, and then the wheels came off in season 5.
I've hoped for years that it would be rebooted. Put it in the hands of completely new people who make a pledge to cut the bullshit. No post-apocalypse crap. No 80's style hyperfantasy. Jettison the rock music. No super-crazy big bad bent on world domination(I understand there has to be a bad guy, but make him or her within reason, tortured by his/her own demons, whatever).
Just focus on what made the series a success...examining what it's like to be immortal and forced to fight others to stay alive, and how you change over time while those you love die around you, or how you maintain relationships with other immortals despite knowing that you might eventually have to fight them. Delve into the mythology. Have a rebooted Methos character. Talk about the Watchers.
There's so much potential there for an interesting TV series or film series. It's a shame that the movies never lived up to it.