The combat system's fundamentally shallow. The bosses are only challenging at all because they're all given large invulnerability windows combined with high damage potential. All of them take dramatically reduced damage from gunfire, in order to force you into melee combat with them. Apparently humans are made of stone, leather, and self-sealing foam, but the moment they become zombies, they turn into papier-mache.
The survivor AI's certainly been improved, but they still have a weird habit of shooting you and themselves as much as each other, and on the 360 rev, it's not rare to see survivors running against walls or getting stuck on short obstacles. Worse, the personality-less drones of the first game have been replaced with a freak parade of clueless idiots. Rescuing most of them is like spitting in the eye of natural selection. When you're told point-blank that the only way to save three particular survivors is to clean all three of them out in a high-stakes game of poker, or a gambler demands a five-figure bribe before he'll let you drag him to safety, a lifelong Buddhist monk would probably react with violence. One girl asked me to strip down to my underwear before she'd deign to follow me to the safe room, and suddenly the room filled with an odd high-pitched whirring. I took a look at my stereo, trying to fix it, before I realized it was Charles Darwin spinning in his grave like a drill bit.
The zombie outbreak occurs roughly three hours before the game itself starts; it's midnight when things first go wrong, and 3:00 AM when Chuck's let loose on the mall. That's just long enough for several people to go completely, irrevocably insane. Fortune City was apparently the unchallenged world capital of smoldering powderkegs, with a workplace policy that gently encouraged the hiring and housing of future serial killers. It was a box that you checked on the application form: tick "YES" if any major disruption to your workplace routine will instantly drive you to homicidal mania, schizophrenia, cannibalism, and/or immediately taking advantage of the temporary end of the rule of law to settle all scores and pay all debts, both real and imagined. If you ticked the box, it was not a deal-breaker. They and you could make it work.
Zombies have an odd habit of suddenly and unpredictably lunging - wait, no, let me start over. They aren't lunging, because that implies motion. The only zombies that are actually dangerous are the ones who can teleport forward and latch onto your neck. You'll effortlessly avoid most of the zombies in a room, and suddenly, one that was nowhere near you a split-second ago will decide that its true place in life involves gnawing on your pelvis.
You will always grab the item next to or underneath the one you actually wanted. There are a lot of bugs, ranging from side missions that cannot be completed to characters glitching through the floor. Several survivors are hidden behind a secret fetch quest, located at the far end of the mall without any clues to their presence whatsoever. The last part of the game, the hour or so before you can get the best ending and fight the real final boss, would be almost insulting if it wasn't murderously difficult. The load times are crazy, mostly due to the frequency with which they're encountered. The female cast is actually kind of embarrassing to watch, because half of them are almost naked and the other half are pretty useless.
Dead Rising 2 has some problems.
Somehow, they don't matter as much as you'd think.
The first Dead Rising was much the same way. It advertised itself as a hilarious sandbox game, where you could use just about anything you could find as a weapon, to dismember, crush, or simply humiliate an endless supply of zombies. Most of the people following the game before its release were expecting it to have a mission structure like Grand Theft Auto, where actual missions would just sit around forever, waiting for you to bother activating them.
When Dead Rising actually came out, it was something entirely different. Your actual enemy in DR is the clock, and the zombies are just running interference for it. From the moment you started a new game, you were dashing from one appointment to the next, saving people here, killing a psychotic clown there, and trying to fulfill the story's obligations along the way. DR let you completely ignore the main plot if you wanted in favor of dicking around in the mall for six hours, although it made it very clear that doing so was a failure condition.
Dead Rising 2 keeps that basic mission structure, although it's not as unforgiving as the original. It even improves on the formula in a few crucial areas. The survivors are much smarter, not that that's a difficult proposition, and having a bunch of them with you can actually be really helpful. The case files are easier to complete, the girl calling you with new missions doesn't force you to talk to her for a couple of minutes while zombies eat your legs off, and the game's schedule gives you a lot of windows where nothing's really going on, allowing you to mess around at your leisure. You can play the entire game in online co-op, which makes pretty much anything better, and the multiplayer is a series of quick minigames that are really easy to pick up and master.
DR2's secret weapon is its willingness to be ridiculous. The Fortune City entertainment complex is full of Easter eggs, hidden areas, silly outfits, and general shenanigans. Every time I get frustrated with the game, and I often do, I tend to forgive it about thirty seconds later when I bury a Roman candle in a zombie's eye socket, or go into an emotional cutscene wearing a Servbot mask and a hula skirt.
The game's shallow as hell, though. There's a lot to do and see, but the game is built to keep as many zombies onscreen as possible, and that means it has to make a lot of sacrifices. The NPCs aren't that much "smarter" than the zombies, so survivors shoot each other and bosses have very simple patterns. The toughest fights in the game involve limiting your arsenal somehow, whether it's due to a boss's greater mobility or because you get your weapons taken away before or during the fight. It's a pretty blatant attempt to paper over the problems with the engine.
The biggest mistake Dead Rising 2 makes overall, though, is being unnecessarily campy. One of the beautiful things about the first Dead Rising is that it played everything straight. You were in a bad situation that was about to go completely apocalyptic, and the people you encountered were all desperate or insane. It wasn't much more than a decent B-movie, with a surprisingly consistent plot and a talented cast of voice actors, but Dead Rising never went for the self-aware laugh. It left that up to you, because nothing sucked all the melodrama straight out of a scene like showing up for it in a badly-fitting superhero costume.
Dead Rising 2, conversely, plays the main plot as a drama, but most of the rest of the game is a farce. Chuck Greene's the straight man to a cast of lunatics and losers, so whenever you deviate from the main plot, you're stepping from a tense action-horror movie to a public-access sketch comedy show. Most of the survivors are morons who come with a laugh track, like the rednecks who barricade themselves inside a room and then set it on fire, and most of the psychopaths are thinly-veiled parodies without any real humor or menace.
At the end of the day, though, Dead Rising 2 is a playground. It's often frustrating when you're trying to play through the actual mission structure, and it's hard not to imagine a number of ways in which it could be better, but it's one of the best sandbox games out there. For all my complaints, I've probably put forty hours or more into it, and that's the best endorsement I'm able to give.