When the original “Kingdom Hearts” was released in 2002, it was something of an anomaly. Gamers were unsure how to approach the then-new combination of Disney and Final Fantasy franchises. Their indecision proved to be unfounded, however, as “Kingdom Hearts” turned out to be a competent action RPG and was soon established as its own franchise.

Now, after a sequel and a handful of spin-offs, the prequel “Kingdom Hearts: Birth by Sleep” has been released for the PlayStation Portable. Does this latest entry in the series match the quality of its console brethren, despite its portable format? In a word: yes.

“Birth by Sleep” takes place about 10 years before the original “Kingdom Hearts,” and follows the stories of a trio of friends training to become Keyblade Masters – Jedi-like guardians tasked with maintaining the balance between light and darkness. Their training is soon derailed, however, as a crisis forces the three to leave their home to face it. It is at this point that the player chooses which of the three characters, Terra, Aqua or Ventus, to control. Because all three characters experience different things, all three stories must be played to understand the full plot.

The game’s status as a prequel creates a unique situation. The story is both self-contained and interesting enough on its own that newcomers to the series will find more than enough plot to keep them interested. Longtime fans, however, will be rewarded with plot revelations that may seem meaningless when taken alone.

The basic gameplay is unchanged from the other games in the series: combat occurs on a 3D plane, controlled by a combination of button presses and the use of menus, using a rotational/lock-on camera system similar to modern Zelda games. The game’s synthesis of earlier Kingdom Hearts games’ combat systems is where it really shines.

Combat revolves around stacking Commands, abilities that affect enemies, to build up a bar called the Command Gauge. Once the Command Gauge is filled, the player character gains access to a powerful finishing move. However, if certain actions are used to fill the meter, the finisher will be replaced by switching to a Command Style. Command Styles, like the Drive Forms in “Kingdom Hearts II,” replace the character’s basic attacks with more powerful variations, lead to their own finishing moves, and can be chained into advanced Command Styles.

Commands themselves are built into Decks for use in combat, much like abilities in the earlier “Kingdom Hearts: Chain of Memories” and “358 Days/2.” Decks can be as simple or as complex as the player likes, allowing flexibility in both abilities and strategy.

In a series first, “Birth by Sleep” includes multiplayer, allowing gamers to link together via Ad Hoc mode and play competitively or cooperatively in standard combat or one of the game’s many mini-games. Rewards earned in multiplayer transfer to the main game, creating added incentive to participate.

Visually, “Birth by Sleep” is a powerhouse. Richly detailed character models match their PS2 counterparts and as combat unfolds, the screen is almost devoured by a cavalcade of different effects working together to create a dazzling light show that serves to punctuate the frenetic gameplay.

The audio is another high point in “Birth by Sleep.” Series motifs find their way into the game, and each world’s combat music is not only evocative of the film it represents but highly enjoyable. On top of this is the game’s excellent voice cast headlined by both Leonard Nimoy and Mark Hammill.

As good as it is, though, “Birth by Sleep” is not perfect. Loading times run a bit long (although this can be mitigated by installing data on the PSP’s memory stick), using menus in the heat of combat can prove problematic (despite a hotkeying system for prioritizing commands) and the lock-on system can fail to maintain focus on an opponent at times.

Additionally, large groups of enemies can create slowdown. Most pressingly, however, is the late-game difficulty spike. The difficulty curve throughout is fairly standard until the last few fights of each character’s story, when the player starts facing opponents that can take dozens of retries to defeat. These tense, difficult fights have a tendency to highlight the combat system’s deficiencies, forcing the player to renew a lock-on or flail through a menu while desperately avoiding attacks.

“Kingdom Hearts: Birth by Sleep” is not a perfect game. It is, however, a very, very good one. It expands the Kingdom Hearts mythos in interesting ways, is a visual and auditory joy and combines the best elements of the rest of the series in its gameplay. In short, it is the best Kingdom Hearts since “Kingdom Hearts II” and is highly recommended.

Genre: Action RPG

Developer: Square Enix PPG 5

System: PlayStation Portable

Release Date: Sept. 7

Price: $39.99

ESRB: E10+

CW Critic’s Rating: 4 out of 4 stars

Bottom line: The excellent story, presentation and gameplay overcome minor technical issues and a late game difficulty spike to create the best Kingdom Hearts game in years.