Doesn't live up to the original, but a great sequel nevertheless.
Basically, you choose to either play as Will or Helen, two 12 year old children from the fictional town of Bellbridge, in England. They have recurring nightmares every night, and in one of them, they find a patch of light, and jump into it, revealing the area known as the Dream Gate. There, they meet a wise old owl, respectivlely named 'Owl', and he explains to them where they are, the Dream Gate, an area in the Night Dimension. Then, they meet NiGHTS, a curious purple Jester-like creature that 'dualizes' with the two children, allowing them to become one with NiGHTS, controlling his actions, and are able to fly. Gameplay is really quite simple; players can use the Wii Remote on its own, Wii Remote + Nunchuk, Classic Controller, or the Nintendo Gamecube controller. NiGHTS can fly up, down, left and right, but is fixed on a course, so you cannot fly off anywhere and get lost. There are seven dream worlds, three unique to each character, and one that both characters must explore. In every world, there is a 'Chase Mission', where the children must find NiGHTS inside a 'NiGHTS Capture' within the time limit (which is easy as NiGHTS is essentially right in front of you), and then Dualize with him to escape from the cage, and chase a 'Goodle' on a bird with a key, to unlock the cage three times. After this you get a boss fight; complete this and you pass the mission. Another mission in every world is a 'Link Challenge' where you have to chase a creatrue called Octopaw, which releases ring, and you must fly through as many Rings and Blue Chips in succession to get as many links as possible. You have five chances to obtain the required amount of links to complete the mission. There are also three platform-style missions where you control the children to rescue NiGHTS in some way. NiGHTS Journey of dreams also brings back the characters Reala, NiGHTS' rival, and Wizeman, the creator of Nightmare, who is the game's antagonist. The game also marks the return of the A-life system, where players can raise their own Nightopians and Nightmarens, and a Multiplayer Mode, where Player 1 plays as NiGHTS, and Player 2 as Reala in the form of a race or a battle. NiGHTS Journey of Dreams also introduces Personas, masks that give NiGHTS special abilites. For example, the Dolphin Persona transforms NiGHTS into a Dolphin, allowing him to swim underwater, finding new places and other secrets. The Rocket Persona transforms NiGHTS into a rocket, enabling him to fly at an extremely high speed. The dragon Persona transforms NiGHTS into a dragon, allowing him to withstand ant winds and reach places he couldn't reach before.
Should you buy this game? Well put it this way: You're more likely to enjoy this if you haven't played the original, but if you're a diehard fan of the first game, then I'd definitely recommend it. You may be annoyed with the minor changes if you have played the original, but it's a great sequel that shows Sonic Team is back to making what it used to make: High quality games that show style.