My entry to the franchise was Highlander 2 which I saw in the theater. I had never heard of the first one, but my Dad and I saw the ad on TV, we were into sci-fi so we thought why not? I didn't really understand it, I didn't hate it. It had a few funny and/or cool bits and a lot of cheese.
So later, in college, I had some theater class where the teacher decided we should watch and discuss a movie, and some guy lobbied for Highlander so that's what we did. I enjoyed it a lot more than the second, it's still got a cheese factor but I see why it became a cult classic. I kept expecting it to end in a way that would lead into the second, explaining how these Earthmen could become aliens by the second film, but it didn't happen. Later I learned the reasoning behind the sequel.
So then Highlander: The Gathering showed up at the video store. We would soon learn that it was a pilot for a new series. It was nice to see Connor again, Duncan didn't really do it for me. Of course I remembered Adrian Paul from War of the Worlds and a lot of other stuff over the years. Highlander is undoubtedly the pinnacle of his career. But The Gathering, with cheesetastic Richard Moll and budget lightning effects, it wasnt enough to gwt me to try the series.
Then the 3rd theatrical flick came out. Again they ignore Connor getting the Prize. The problem is they made a series out of a movie that was all about the final battle of its mythology. You can't really follow it. Van Peebles doing his best Kurgan gravel-voice. I say skip this one and watch Lambert and Van Peebles in Gunmen instead. Now that is a cult classic.
I didnt see the 4th film until much later, I was on a completist kick. Mediocre, seems like an episode. So after killing Heather, killing Brenda (twice), now they have to dig up Rachel and kill her too? Doesn't pay to be a lady friend of Connor MacLeod. I might have just watched for the Edge appearance, I was big into wrestling back then.
Eventually I got the Director's Cut of the first movie and the Renegade Edition of 2 (and the Special Edition, natch). I really appreciated what a good visual director Russell Mulchahy is. Even 2, it's so well staged with big sets and locations. I like the behind the scenes video where they talked about needing a train track running through a downtown area for one setpiece. Instead of laying track in an existing downtown, they found ab existing track out in the sticks and built an entire town around it. This movie must have been leaking money, no wonder the insurance company took over production. Then there's the "Gone With the Wind" scene where they keep zooming out to reveal hundreds, no thousands of victims in the UV burn ward. And it was cut for time in the theatrical release. What a testament to wasted potential this movie was. Too bad it was all at the service of such a crappy plot and script. I rewatch it almost as much as the first. It's the worst movie I've ever loved.
I can't believe that Highlander 2 wasn't the movie that derailed Mulchahy's career, but The Shadow, which was a decent movie.
I did see Highlander 5. What a mistake.
Original continuity: first movie, Connor wins the prize: THE END
Second Continuity: HL 1 and HL 2
Third Continuity: HL1 but revised so that yes Connor took down Kurgan but it wasn't the final gathering for the Prize, and the TV series plus its spin off.
Fourth Continuity: HL 1 and HL 3, though HL3 occurred when Season 4 of the series started it did not link to the series.
Fifth Continuity: The third continuity listed above plus HL 4 and HL 5.
The third continuity is I believe the one that is considered canon, HL 4 and especially 5 were so negatively received that both may well be disregarded. I know for a fact that HL5 definitely is.
Now continuity 6 is in the works with a reboot of the original movie.