After you finish the single-player portion of the game - which is a little shorter than it should be -- you can play through the game to get a better ending. The basic vanilla ending is okay, but putting the effort in gets you a far more satisfying conclusion. There are plenty of items to collect as well, and since they carry over, you can collect all the goodies that are hidden in the game pretty easily.
When you beat the game you also unlock secret characters and some extra play modes. There's also an interesting multiplayer component that can be played locally via Wi-Fi or Nintendo's Wi-Fi connection. Multiplayer consist of boss rush mode, a coop mode where you race to the end of a level while battling enemies and a smattering of bosses.. There's also a fun little store mode where you can either set up a shop or buy from other player's shops , giving you yet another way to get some cool and unique items.
Castlevania: Portal of Ruin is a great example of what's possible on the DS, despite the fact that the game really doesn't go out of its way to utilize many of the DS' marquee technologies. The game is wonderful simply because it delivers a pure unadulterated classic Castlevania experience that looks great and plays like a dream. If you even have a passing fancy in this popular series, Portal of Ruin is worth owning.