I've only seen BTF-2, so I guess I'm a bit out of the loop on this....
But I liked it as much as I saw - will try seeing parts 1 and 3 when it next comes on TV.
What a coincidence, they just showed each Back to the Future over the last 3 nights on TV. I liked 1 and 2 a lot, but 2 got a little bit too weird at some points, so it's 1.