I <3 the first movie its totally awesome!
I also really liked the series and how it expanded and explored the Highlander universe. One of the things i really loved about the series was was seeing how Duncan managed to have friendships with other immortals like Amanda and Fitz and Methos and the flashbacks showing how these friendships developed over the centuries. The writers had the opportunity to explore what it meant to be immortal in more detail than in the films.
Though i did find Duncans mortal girlfriend in the first couple series a tad annoying. Imho when it came to female characters Amanda was a lot better as she could hold her own in a sword fight, she possesed a moral greyness that was refreshing plus her bickering with Duncan was more amusing than his angst with the mortal girlfriend. You could tell that Duncan and Amandas friendship was one that had developed over centuries by how well he knew her and how she was able to annoy him in a way no one else could.