First, let's get the obvious out of the way. One, yes this isn't a sequel, two, yes the guy's name is Colin, not Connor, and three, yes the line "There can be only one" is used. The film remains true to the spirit of the original Highlander but is unique in its own right and is far superior to the sequel films it produced.
The protagonist this time around is a new MacLeod named Colin, whose wife is killed by fellow immortal Marcus Octavius during the time of the Roman Empire and Colin swears revenge, beginning a centuries long quest to kill Marcus because through a series of incidents, Colin is unable to kill Marcus, thus leading the story to a post-apocalyptic New York (no surprises there) where Marcus is now a brutal ruler opposed by rebels living in the abandoned and decaying city.
Most of the story is set in the future but in the true spirit of the Highlander franchise, much of Colin's existence is fleshed out in a series of flashbacks, showing him and Marcus fighting each other through Waterloo, Boxer Rebellion, WW2, etc, and the attention to historical detail is immense. There are some great sword sequences and dialogue, particularly between Colin and Marcus and the animation, art and special effects are spectacular.
Although the plot isn't original, this is still a great film to own, if you liked the original Highlander film, Ninja Scroll or sword fighting movies, this definitely deserves a spot on your DVD shelf.