Nearly every way better than the original game.
Pikmin 2 starts right after the first Pikmin when Captain Olimar managed to escape from a strange planet with helpful beings called pikmin in it. Back at home Olimar’s ship is confiscated, because his employer is in debt for 10 000 pokos. Now it’s up to Olimar and his apprentice Louie to go back to the pikmin planet and collect enough items to cover the debt.
Graphically Pikmin 2 is that same colorful quality, which looks nice but not real. Luckily this time around the environments are more complex and detailed. Sound on the other is pretty much the same deal as before and can get annoying at times.
Gameplay has been improved in many ways. First thing is that now there are two playable characters, which makes multi tasking a lot easier and you can change the command between Olimar and Louie at anytime. This also makes many boss fights easier, because you can split your troops in two in order to be more effective. There is no 30 day time limit anymore, which makes exploring the game world a lot more fun and rewarding.
There are also more pikmins to strategize with: yellow ones are now immune to electricity, white ones stand poison and purple ones can lift heavy objects. These white and purple pikmins can only be found in many caves throughout the game. Caves act like dungeons in Zelda where you go in with a set of party and do your mission with its help all the way through. Your main mission in Pikmin 2 is, as mentioned, to collect different items and they are all practically junk like giant batteries and oranges. This is interesting and funny.
The original Pikmin was quite short but this is not a problem in Pikmin 2: it took me about 36 hours to finish it.
Pikmin 2 is a great and nearly every way better than the first game.