Core is not a masterpiece but it passes the time away.
As far as first person shooter goes, the controls are awful! Using the stylus is a big pain BUT once you get used to it its not much of a problem. The story wasn't great but to be honest for the price i paid i didn't expect an amazing story.
This game gets pretty tough in some places but not so tough that you will be stuck for weeks, i would say the difficulty is about right for me( and i suck). Graphics are awful but again its a ds game, i never get my hopes up!
The multiplayer keeps your attention a lot more then the single player, iv played several times with my friends and its pretty fun.
Overall i didn't mind this game, i would never pay more then $10 for it, it deserves a lot more then a 3.5/10 though!