This game is a huge disappointment to me, as the original was one of my favorite games on the N64. It's not that there's anything particularly wrong with Perfect Dark Zero, it's just that there's absolutely nothing spectacular either.
The single player is a complete drag; it's just going through the motions. You could play a level from any other sci-fi shooter and it could fit right into PDZ. The game is mediocre for pretty much the whole way through. The A.I. isn't broken, but they can't do anything smart other than run at you and shoot. The graphics aren't terrible but they're unspectacular.
My point is, though it's possible to have a good time while playing this, it's only if you're in desperate need of some shooting action and you've played the crap out of CoD or Halo. There honestly isn't any reason you should be playing this game if there's another shooter on your shelf.
The single player has some problems that really need to be fixed. The levels aren't corridors, but they might as well be. There's only one path you can take through a level, and if you stray off that path you get lost, even when there's an arrow on the floor guiding your way. Another problem with it is the A.I. I talked about it before, and even though your enemies can give you some trouble at times, it's just because they're programmed to be overly accurate. The enemies in this game don't take cover, they don't try to flank you--they pretty much just rush you and hope they live to tell the tale. So, while you're draining health due to their over-accuracy, it's intense, but only because you're draining health. The opponents just really don't do anything special.
The graphics are sub-par. They have the "next-gen" look, if you consider overly shininess on everything "next-gen." It's really ridiculous. Sure, I expect a club owner's SUV to be shiny, but I don't expect desert sand and canyon walls to be. That's just pushing it.
The game plays ok, if a little slow. It's basically what you would get if you took the default sensetivity on Halo and cranked it down a few notches. Then took away the jump button. Again, they work: but they aren't anything special.
And there lies the game's biggest fault: Its mediocrity. Everything works; nothing shines (except every single frickin' surface in the game). The original was a masterpiece in its time, but this game is stuck back in that era as well.