Teddman said:
If I've never played the original, would you recommend skipping directly to the sequel? Does this game pretty much make the first one irrelevant or redundant, or do they cover different, er, ground?
Technically, the second is superior in every respect, and to that extent it makes the first redundant.
However there is a huge difference in atmosphere between the two.
In Endless Ocean, you are alone with the ocean except for your mentor (or tormentor) Catherine other characters play only minor and remote parts. In the game nature takes its course and you are mostly an observer it is a vision of you in eternity and the challenge is how you cope and how you pace yourself and task yourself in your intimacy with the sealife. It is very sandboxy, and doesn't order you around so much.
In Endless Ocean 2, you are part of a team of developed characters with an objective or several in mind to the extent that sometimes the creatures are an obstacle course rather than just being themselves. The focus is more on the human endeavour than on the ocean world, and that gives a completely different feeling to the game. It's more structured, more task-oriented.
(those are extracts from my GameFAQs review)
In addition the first game is more real - pretty well everything in it is obsessively accurate to the extent that even the in-game myths are real myths.
The second takes more liberties with reality for the purposes of the game.