Title: Final Fantasy: Dissidia
Genre(s): Action/Fighting with RPG elements
Platform(s): PSP
Release Date: December 18, 2008 (JP)
Rating: 7.5/10

Story:

Game Features:

• Destructable arenas, and free roaming environments for 1v1 real time action (option menu driven mode can also be unlocked).
• Features playable hero and villain characters from FFI through to FFX, with bonus characters unlockable.
• 2P multiplayer through PSP's connection system.

Main Characters:

Heroes

• Warrior of Light (FFI)
• Firion (FFII)
• Onion Knight (FFIII)
• Cecil Harvey (FFIV)
• Bartz Klauser (FFV)
• Tina Branford (FFVI)
• Cloud Strife (FFVII)
• Squall Lionheart (FFVIII)
• Zidane Tribal (FFIX)
• Tidus (FFX)
• Shantotto (FFXI): Unlockable

Villains

• Garland (FFI): Unlockable
• Emperor (FFII): Unlockable
• Cloud of Darkness (FFIII): Unlockable
• Golbez (FFIV): Unlockable
• Exdeath (FFV): Unlockable
• Kefka Palazzo (FFVI): Unlockable
• Sephiroth (FFVII): Unlockable
• Ultimecia (FFVIII): Unlockable
• Kuja (FFIX): Unlockable
• Jecht (FFX): Unlockable
• Gabranth (FFXII): Unlockable

Review:

• Gameplay: 8/10
• Graphics: 9/10
• Sound: 8.5/10
• Length: 6/10
• Replayability: 6.5/10
• Overall: 7.5/10

Gameplay: I have few complaints to make about the gameplay of Dissidia.
With the restrictions of hardware, screensize and buttons, PSP actions games that try to utilise a more complex battle system have all but failed in making an intuitive yet effective way to bash the bad guys.
So, what Square-Enix (not by any means new to the PSP scene) rightfully did, was incorporate a simple yet intelligent battle system.
The RPG element sorts out not only your equipment and items, but also manages your skills outside of battle, so you don't need to wrestle with menus and other nonsense in the heat of battle.
You have only two attacks; the O button initiates an attack which steals your opponent's "Brave Points" and adds them to your own, while the Square button attack causes direct damage to your opponent's HP bar using your accumulated "Brave Points". 
The strategic element, is mainly derived from whether you choose to "break" you opponent's "Brave Points"  to 0, giving you a bonus to your own accumulation of points while also leaving your opponent vulnerable, or to chip away at their HP bit by bit without wasting time on their "Brave Points" other than to prevent them from bringing your own stock to 0. Also adding to the strategy is your usage of the stage elements, preparation and your chosen skills/equipment.
There is an inclusion of a "limit break system", which is activated by filling your "EX Gauge", and enables the use of your character's EX mode, resembling that found in your character's original game.
Progress between battles is also quite simple, and you move around and encounter enemies on different stages made up of squares, each move using up "Destiny Points" (DP). You can spend all of your DP to collect items and fight all the enemies, or save it for bonus points at the end of your character's campaign,  used for unlocking more skills and equipment.
Multiplayer is simply a 1v1 battle between you and your mate's chosen character.
 

Graphics: The graphics are excellent, making full use of the PSP's often underestimated GPU. The colours are vibrant, and the characters highly detailed. The only area which can seem lacking at times is the texture detail on the levels and characters themselves, but this can't be helped due to the portable hardware limitations. Overall, the graphics are a step up over many 3D titles on the PSP, and on par with the best of them.

Sound: The music is a great selection of memorable tunes throughout the series. Each character's campaign is accompanied by the theme of their original FF game, while the battles are accompanied by battle themes chosen from normal and boss battle music, also from the original FF games. Sound effects are clean as well as accurate, and match the visuals well.

Length: There's a catch here. Technically, the game is quite long, with each hero character having their own campaign to play through. The reason this didn't get the game a very high rating however, is that much of the gameplay is repetitive, and unless you are a Final Fantasy fanatic (and I mean, all the games, not just FFVII), you probably won't be very interested in playing through the unfamiliar character's respective stories.
This could be avoided if the game had a strong story bring all of the characters together, but unfortunately Dissidia falls flat on it's face when it comes to plot.

Replayability: There is a lot to unlock, and as you might expect, a lot of leveling to be done for those who find that kind of thing enjoyable. However, for the casual player, the only replayability lies in the mulitplayer which won't take it very far, given the imbalances and the steep difficulty curve warding off beginners for pick-up matches.

Overall: It's definitely a must-own game for fans of the series, and not a terrible choice if you're looking for an action game even if you're new to the series.