Kingdom Hearts: Birth By Sleep is a prequel that delivers graphically, takes a nose dive story and character wise.
Birth By Sleep is cut up into three chunks with three different main characters. Aqua, Terra and Ventus are keyblade wielders and training under master Eraqus to become keyblade masters themselves. Aqua and Terra are ordered to travel to other worlds to rid them of a new threat called "Unversed". The game presents these monsters as the main enemies to defeat as were Heartless and Nobodies in other installments. Ventus however is not allowed to leave, but leaves anyway to travel after Terra. Aqua is ordered to bring Ventus home.
The stories of the three main characters can be played in any order, but selecting the default displayed order is most likely better for the overall enjoyment. A time-line is displayed on the main screen after finishing certain parts of the game so you can see who visited which world in what order.
Now having three characters and three stories to uncover in a single game sounds great, but you'll soon find that in its execution lies its flaws. The three characters all visit the same worlds, talk to the same people and battle the same enemies and bosses for the most part. Come your third play-through the worlds and characters feel regurgitated and the entire thing becomes a mind numbing experience as you're forced to upgrade your skills three times in a row.
The battle system is tweaked from its previous installments and is in fact a lot better. Spells and abilities do not cost mana, but will be timed out after use. Another ability will take its place so you can use it immediately. You can also scroll through available abilities fairly easy. This way the ability system which was somewhat of a hassle in the earlier games, actually holds on to the pacing of the battle system. Depending on how you setup your abilities at from the main menu you can basically lay in a world of hurt on your enemies without actually looking for that particular ability or try to figure out which short cut you put it under. Characters can also change their "command style" to power up their abilities and moves like Sora was able to transform into Valor and Master form in Kingdom Hearts 2. Transforming is easier and more frequent though. Depending on what abilities you sue a bar fills up. When it is full you will either use a finishing move or transform into a stronger Command Style.
New is D-Linking. An ability that consumes a separate D-link bar and allows you to use abilities from characters you have D-linked with. This allows a more flexible set-up, but the game doesn't require you to use this at all. In fact it looks more like they tried to add something new just for the hell of it. It sounds useful, but D-linked character abilities are usually far less powerful than your own, depending on how you leveled your abilities. D-linking is comparable in execution to the summons in the other game. In fact they're just as useful or useless depending on your playing style.
New is also Shotlock commands. This allows you to target one or more enemies for a "rush attack". Shotlock attacks bassically decimate any enemy and bosses. Shotlocks use a different bar, which is increased by hitting enemies.
Abilities have levels and can be levelled up by having them equiped and defeating enemies. An abilty that has attained its maximum level (3 for low level abilities and 6 for high level ones) can be combined with other abilities to form completely new ones. If you add certain items (stones and crystals) you pick up during your adventure you can also add stat enhancing properties to the ability. this properties become permanent once you have maxed out the abilities level.
This sounds very interesting and it does add some punch to the basic character setup, but its a time consuming exercise. The main cause for this is that you cannot see what you're creating when combining abilities. You also can't see what property will be added either. Combine those random with the fact that you can't simply load your game from the in-game menu and you have an ability leveling system that is far more annoying than useful. Loading a game takes over a minute even with the full game installed. This means you can only try out about 50 combinations per hour. If I tell you the game can create over 10.000 combinations you'll understand why this system doesn't work as well as it should. Maximizing your character shouldn't require a walk through or FAQ, but without one your characters will never reach their full potential within a normal persons lifespan. And when facing this leveling up system three times in a row you can be sure you'll be bored of it long before it is over.
Kingdom Hearts games have always presented itself as a cross-over between Final Fantasy and Disney. As such you'll be disappointed to know that only one character from Final Fantasy is present. And if it weren't for his name and outfit you wouldn't recognize him at all. His personality has had a make over that would put (un)pimp my ride to shame. Luckily there's plenty of new and returning Disney characters and most of them are a joy to watch. Worlds you visit are a combination of worlds you visited before and new worlds. New worlds include Sleeping Beauty, Snow White and Lilo and Stitch. Most of these Disney worlds are developed well and contain believable characters. Most of the female voices however are bad. I don't recall the original Snow White voice being performed by a man who's been kicked in the groin a couple of times. Luckily these characters have only a minor role, so they won't affect your gaming experience much.
Graphics wise the game is great to look at. Character details and environments look great. A note to gamers, turn on the 32-bit color feature in the menu to enjoy the game to the fullest. Otherwise you'll be playing a 16-bits game. Loading times are acceptable except when it comes to the menu. Bringing up the menu can take up to 10 seconds. Even after the game is fully installed it will still access the disc numerous times all the while slowing down your game. On the whole though it doesn't have much impact on the game itself. Battles run smoothly and frame rate generally is above the minimum threshold.
Out of all the playthroughs Ventus's is the most interesting. He has interesting mini-games, fights the most unique bosses and obtains more interesting abilities in his normal storyline. When looking at the characters Ventus's voice actor is probably the best. Probably also because it is the same voice actor as Roxas from earlier installments. Terra's voice actor isn't bad as an actor, he's just not right for the part. Aqua's voice actress is abysmal in her performance. Her voice sounds good and matches the character, but she sounds like she has no clue to what voice acting means. Everything she says comes out with the wrong tone, emotion and generally sounds like she's totally bored of the game before she started. Its a shame because out of the three Aqua is probably the more interesting character. Female characters usually are since they do not have the usual "I need to be stronger" attitude.
The story, like said before, is a prequel to Kingdom Hearts. Therefore characters from the previous games are present including a younger version of Sora and Rikku. A lot of what goes on doesn't make sense though. King Mickey's ordeal is uncovered, but with it it loses the mysteriousness it had in the earlier installments. Sora and Rikku's rise to Kingdom Hearts stardom is somewhat uncovered, but it is done so in such a crude fashion that you're probably wondering what the hell is going on.
Birth by Sleep probably is a prequel that shouldn't have been made. It delivers great looks and a flashy battle system, but is offset by a mediocre story and dull main characters. All of this isn't bad, but when it touches the foundation of the Kingdom Hearts universe it leaves a nasty mark that will require a lot of effort in Kingdom Hearts 3 to fix. So to conclude Birth By Sleep isn't a winning team, but because of all the effort put into it nobody will notice.