I have played through both games and SuperPac's assessment of Crimson Sea 1 is fairly accurate. It is Dynasty Warriors with guns, a sci-fi twist, and Phantasy Star Online offline gameplay. The story may not be super incredible but it functions with the amusing cast in the game. Sho and Shami were my favorite characters and for a little piece of trivia, the name Shami means fire.
I really liked the art direction and look of the levels as well as the cool aliens I was bashing to death. Every level for the most part looked different and helped in immersing me into this sci-fi universe. The camera was very unfriendly because it wouldn't allow for much rotation. The movement controls at times were rather tanklike.
For many people, such an issue would kill their interest in the game but I stuck with it to the end because it was entertaining enough to finish and I prefer not to give my opinion on a game until I beat it because I believe that only after one has completed a game do you have b***hing rights. The ending was ok too. I give Crimson Sea 1 a B.
Crimson Sea 2 on the other hand was a shot in the foot for Koei. The developers pretty much degenerated Crimson Sea to a repetitive dungeon romp. They also moved it to the PS2 because Crimson Sea 1 wasn't exactly a big seller on the X-Box and Koei thought by moving it to Sony's console, they could achieve more sales.
There were improvements made such as a fully rotational camera, more flexibility of movement, faster attacks, combo tricks, and a new playable character Feanay. There were also downgrades made in the form of a cursory story that pretty much excluded all the characters except for Sho and Feanay, a forced love relationship between Sho and Feanay, an option to see cutscenes from Crimson Sea 1 but with lesser graphics and certain scenes cut out, levels that just recycle a few templates (and are boring, ugly, and monotonous to boot), no cool bosses, weaker graphics, and a dissapointing ending to boot. I give Crimson Sea 2 a C.
In a nutshell, Crimson Sea 1 has an iffy camera and tankish movement, but everything else is fun. Crimson Sea 2 has better gameplay and camera movement but is inferior in every other area.