A very fun combat and leveling system plus some good graphics make this a solid game.
Combat System:
The combat not only looks nice and flashy, but its also quite fun and involves a lot of skill. The point is to hit the opponents with normal attacks to increase your own bravepoints and decrease theirs. Do it enough and you could "break" your opponent, and get a load of brave points to do your second attack, which directly affects HP. Its a well developed system, made even more fun by the fact that there is such large stages where you can dodge, run or chase the opponent.
There are 24 characters in all I believe, which is quite a large roster, and most of the characters are quite different from the other. This adds a great deal of variety to the game, for there are specific tactics to be used for each character. Unfortunately, unlike a game like... brawl for instance, the characters aren't equal at all. A couple, like the onion knight, are extremely underpowered, while a couple others are too good and you'll be seeing those the most often in pvp.
The combat system, as good as it is, gets quite tiresome later on at least in my opinion. Its not nearly as addictive as that of brawl or other games.
Story Mode:
There is no real story to speak of, and the whole thing really becomes a chore, and its even more annoying that the damn thing is more or less mandatory. Some storylines are more interesting than others but all in all the whole thing is quite boring.
Leveling:
There are several leveling tricks, but its quite boring lvling your character to a sufficient level to compete multiplayer.
Graphics:
The graphics are overall quite good. The stages could look better, but who really cares about them. Its the characters that are important, and they look great.
Online:
With no real storymode and single player getting boring quickly, you'll turn to multiplayer quickly. Thankfully, the multiplayer is quite fun and you'll get several matches quite quickly. There are several people playing online, though only at specific times.
There is some lag online, but not too much.
I have noticed there are some cheap tactics that are used often in multiplayer, but thats a common proble.
Overall Dissidia is a great game which is sure to satisfy fans. For non-fans looking for a good fighting game, Dissidia is good enough for a while, but will get tedious quite quickly.