Absolutely LOVED 1 when I played it on the SFC back upon release. It's a short game that you can tell a lot was cut out of, and suffers from a lot of backtracking, but the combat was pretty interesting for the time, as well as the crafting and skills system. Storyline was a nice change from RPGs of the day, even if it was much too Star Trek-y.
2 is one of my favorite games of all time and by far the peak of the series. The skills/crafting were at their absolute best here, and offered you a ton of freedom. There were lots of side quests and optional minigames, whole characters that would/wouldn't join your party (not to mention, the cast was a bit more interesting than your usual RPG cliches), multiple (short) endings based on how you acted toward your party members. Combat was pretty frantic and, although a bit repetitive this day and age, was awesome.
I can't say I outright hated the 3rd game, but I expected the world of it after 2... and was extremely disappointed. Thought the dungeons were waaaaaay too long, combat felt slightly "off" (especially as enemies kept falling down rendering them unable to be hit), the skills and item creation system were extremely neutered, and of course the infamous plot twist. Definitely my least favorite in the series.
Even though everybody hates the 4th game, I had a great time with it (especially compared to #3), as I have an extra high tolerance for uguu. I thought the combat worked out a lot of the kinks the 3rd game suffered from, not to mention it was extremely fast-paced, more sci-fi than the rest of the series, and I liked "blindsiding" enemies. Save points were also spaced too far apart. Item creation worked fairly well, I liked how you would 'brainstorm' new recipes, even if grinding for drops got annoying.
The team definitely has some great ideas in terms of gameplay systems, and I love sci-fi/space travel in games, but needs much better writers and needs to add more save points in their games.
