Studio Japan really did lots of improvements during just one year. Having played the original Patapon for 40+ hours, I see myself playing this game for even longer. Much has stayed the same, but the several improvements were very welcome.
For one thing, reaching Fever mode has been made easier. No longer does one need a perfect timing of four consecutive beats in order to reach Fever. Perfectly timed beats are still needed to charge the meter that determines when Fever starts, but it's a lot less frustrating than in the original.
New fighting classes include bird-flying Toripons, structure-destroying Robopons and magic-wielding Mahopons (haven't gotten those yet). Also there is Heropon. A leader of the battle group of sorts, he will resurrect automatically after dying, it takes a moment, but still. If you can beat the rhythm with perfect timing (4 consecutive beats), the Heropon will activate his superpower, which depends on his character class. Personal favourite is a Tatepon Hero which activates invincibility for three rhythm rounds.
The patapons' evolution has been totally changed. Now there is an evolution tree, with around 15 different patapon types, all with 10 experience levels and different strengths and weaknesses. Maxing out your soldiers will take eternity. Hoarding level 4 and 5 materials to get the best patapons is still a part of this game, but even the mediocre patapon types will be useful after levelling them up a bit.
In the original game, even the worst additional weapons and armour were scarce at times. In case you missed them in the "storyline" missions, you had to start fighting against the bosses, in hopes of them dropping something useful. Actually, once you had finished everything else, you could only hunt and fight bosses. Now there are also fortresses to conquer. You may play certain levels with increasing difficulty, where the main point is to advance in the level, killing enemy soldiers and destroying their fortifications. This will give some new gear. Nice addition.
There is also a multiplayer mode, haven't been able to test it with a friend, but it's possible to play this MP mode alone. The goal is to carry an egg with a time limit across different stages. Some stages will have you fighting against bosses, others are the conquered fortresses from the storymode. Killing to boss and destroying the fortress will give you access to the ending minigame, which can net you some nice materials and/or equipment.
Also the minigames from the original are back, now with different difficulty levels and increasing cost in money. It's a lot more useful to play them now.
At the moment the best game for PSP released in 2009. Highly addictive.