I've only played all the way through 2. However, I have all five games and the visual collection. Here are my thoughts on them.
Part 1 seems good for a very early CD-ROM RPG. I made it a little ways in, the design is nice, the music is decent. I liked what I played.
Part 2 is a good game overall, great art, story and character designs. The actual gameplay both battles and exploration leave a little to be desired but overall I like it more than Dragon Slayer to make it the best US released JRPG on the Turbo.
3 I got a little ways into and looked a lot like 2 but perhaps a bit more polished.
4-1 Had about 40 minutes of digital comic stuff to wade through, talking to a chick at a pool. Talking to another chick at a pool, going to a meeting. I felt like I was at work. By the time I actually got to control my character it was like an hour in and I didn't know where to go.
4-2: Started off with a digital comic although not as long of one. I couldn't figure out where to go after a certain point and gave up.