True to the Metal Gear series, but not for people unfamiliar with Metal Gear Solid.
The gameplay mechanics is like a RPG card game and a Tactics Video Game combined (based on games with the word Tactics in its title such as Final Fantasy Tactics or the new Lord of The Rings Tactics game on PSP).
Most people I've talked to say that they are disappointed with the fact the game doesn't have the same gameplay mechanics as the Metal Gear Solid games. I thought it was a good change and was very fresh and original (they have a Metal Gear Solid game for the PSP in the works that has the familiar gameplay mechanics of previous games and some new surprises).
One of the best things about the visuals in this game is it has great Japanese cartoon (anime) drawings to tell the plot instead of the typical CG movies people see in most games.
People that are not familiar with the Metal Gear Solid series will have some trouble figuring out who the characters are featured on the different cards in the game. If you've played Metal Gear Solid and at least briefly played Metal Gear Solid 2: Sons of Liberty on the Playstation 2, then you should be fine.
I think Metal Gear Acid is going to be an underappreciated and overlooked game by most, but people should at least rent it and give it a try. This one might get the attention it deserves later on. Metal Gear fans whom want to see some more storyline that is true to the Metal Gear series should definetely pick this one up. Can't wait for Metal Gear Acid 2!