Having been a fan of NiGHTS since its original release back on the Sega Saturn, I can tell you a LOT of love went into this port. In addition to the original game itself, included also is the rare and coveted demo disc Christmas NiGHTS, opening up unlockables and a varient of Spring Valley primarily centered around Christmas (though the theme sometimes changes depending on the holiday/date, such as April Fools, Halloween, summer, Valentines, etc). This alone makes this port worth it to the die-hard fan, but on top of this, you've given the option to switch between the original Sega Saturn graphics, or the graphics of the formally Japan-only PS2 remake.
For those of you unfamiliar with this title, you can choose between to play as either Claris or Elliot, two children whom by day struggle to overcome their fears, and by night aid NiGHTS in overthrowing the king of all Nightmare, Wizeman. As you fly through linear circular stages, you'll collect orbs and other goodies, destroying captures that hold Ideya - raw dream energy - that had been stolen from the two children. Its story is left intentionally vague to encourage the player's own imagination to interpret the events. There are also many goodies and easter eggs to be found hidden around, including the curious Nightopian AI (these being creatures that breed, grow, die and can even hybridize with enemies within the level). At the time of its original release this game offered groundbreaking techniques in graphics and gameplay style, giving it its own place in history and recognized by many as an unofficial secondary mascot to Sonic Team.
And now for the downside. Unfortunately, the game is incredibly short and can be 100%'d in only a few hours, though the extras help to provide some replay value. Also, while the controls, for the most part, are pretty tight there are areas where NiGHTS becomes difficult to control - particularly areas like the bobsled, mermaid and rail portions from their respective levels.
Still, despite those problems, for the price and what it comes with, I would consider it well worth it and highly recommend it to anyone interested in a timeless masterpiece and a piece of gaming history. If you're still unsure, I would say to consider waiting for a sale. Either way, NiGHTS into Dreams is well worth having in your collection.