Just finished a complete straight play-through of the King's Field series. Such a freaking awesome series. I started with an English translation of the original Japanese-only King's Field title, through the Sword of Moonlight program, so it wasn't quite the same game but close enough. I then played through King's Field 1 (U.S.), KF 2, and finally KF: The Ancient City all one right after the other. I've played through all these games before, but never before all of them, one right after the other like this.
The original Japanese-only King's Field was my least favorite in the series. That could have a lot to do with the fact that I wasn't playing it as originally intended, and was instead playing the English translation through The Sword of Moonlight software. The enemies looked weird, the movement of the character wasn't quite right, it was much shorter, and the enemies were a lot tougher until you got to higher levels (which was probably their way of trying to stretch out the short game).
King's Field (U.S.) is a great entry in the series, too. Well worth a play-through for anyone interested in these sort of games. Not very story-driven, more exploration-driven (which exploration-driven is still a good thing), but not quite as large as KF II or KF: The Ancient City.
King's Field II still stands out to me, head-and-shoulders, above the rest in the series. There's a great storyline going on there if you pay attention to what the characters are saying and all the clues laid out before you. It ties the other 2 games before it into it's story wonderfully. And the level-up system of the magics, character, and Excelletor Sword make it even more rewarding when leveling-up than the other King's Field games. Then you add in the unique weapons and armors and larger areas than the 2 games before it and it's a masterpiece for it's era.
King's Field: The Ancient City on PS2 definitely looks the best, though. But them why shouldn't it when it's on the PS2 and the others are PS1 games. It's also the 2nd best game in the series, in all other aspects, as far as I'm concerned. Not as story-driven as KF II, but at the same time it's probably the most exploration-driven game in the series which gives it all kinds of points in my book.