It's a fun fun game. It's very newbie friendly, as it took me 15-20 hours on normal mode (at the beginning you choose between easy or normal, and once you beat the game you unlock Extreme, which is what I'm playing again.) Online rocks as any weapons you get in single player mode you use online. Plus, you can recruit soldiers to take with you online, (through both searching on wifi and ingame people) so when one of your characters die, you switch off. If you like Subsistence and are planning on buying Guns of the Patriots, you'd need to beat this one to understand why Snake is in Guns of the Patriots. Plus, it reveals who saves the world in the future. Which I'm not saying. Here's two reviers:
Game Informer's Review
Game Spot's Review
And the all knowing thread of everything you'd want to know about this game :
Informational Thread
So you don't just need to take my word for it. If you own a PSP this game is a must have. Plus, it's not Metal Gear Acid, it's the MGS Subsistence Engine but just a brand new game, but Snake is the same model, but with less polys and a lower texture resolution.
Hope this helps on your decision!
Drew
please forgive me about my forum name.