I finally watched IV a few months back. It's ok at best, but not something I would go back to often. I might even watch the remake more than this, just for the laughs that movie gives.
The first three make for a pretty awesome and high quality trilogy. Not as crazy about 3 as Alex, but I still like it a lot and at this point, I'd give Part 1 a 10, Part 2 a 9, and Part 3 an 8 or so. I haven't seen the sequels over and over because I got into them late, but man, I already feel super nostalgic about them. It's like I'm entering another phase of getting older and now movies I saw a couple years after getting high school are becoming very fond memories. It's kind of cool.