As bad as you've heard? No way. A perfect game? Meh...
Shadow The Hedgehog tries to explain the title character's reappearance after "dying" in Sonic Adventure 2. This is attempted by giving the player complete control over the storyline, up until the final story, where you do the usual Super form vs. powered-up cheap baddie showdown, and find out the truth about ol' Shadsie.
The game basically plays like the previous entry, Sonic Heroes, except without the teamwork gimmick. Of course, Sega is all about gameplay gimmicks these days, so what do they do to replace the lack of a teamwork feature? Give a cuddly hedgehog the vocabulary of a mainstream rapper and an AK-47, of course! Or should that be "fo sheezy"...? I can never keep track of hip-hop trends, but I digress. By doing this, Sega received a huge backlash from the Sonic fanbase who felt they were ruining the franchise by giving Shadow access to guns and vehicles, especially when he's toted to be the "Ultimate Lifeform" and shouldn't need those things. My personal opinion is as long as they don't give Sonic a glock, I can deal with it, but thats just me.
Anyways, back to the game. Naturally, the guns are a huge gameplay element. While I feel they were unnecessary, the gunplay actually is very smooth, with an almost consistent auto-aim feature. The turrets and melee weapons, however, are utterly useless. By the time you actually swing the energy swords, you've already been knocked around a couple times. And just avoid the gun turrets unless you need them to complete a level objective. The only time they're actually fun to use is in the rail-shooter level, Lost Impact. The basic gameplay is about the same as Heroes. You have your usual homing attack and triangle jump moves, along with Shadow's Chaos powers, which grow depending on what you do in the levels. Attack the good guys, and you'll gain access to the atom bomb that is Chaos Blast. Beat up on the baddies, and you'll get Chaos Control, which warps you through a segment of a level. I've heard alot of people complaining about a massive amount of slowdown in the PS2 version, but I rarely experience any. The only time it really happens to me is when there are alot of things happening on the screen at once, and that happens in even the best games, so I'll let it slide here. A major complaint for me is the sometimes shoddy collision detection, and the "trap doors" I've encountered in some levels, especially the ARK ones.
Graphically, I've seen much better. The CG scenes are great, but the gameplay graphics aren't what I'd expect for a PS2 title these days. Of course, the Sonic games have never been a graphical masterpiece, so, I wasn't entirely surprised. A major complaint, graphically, is the real lack of originality. There are a few levels that really stand out on their own, but most of the levels are rehashes of each other, a huge sign of laziness by the Sega design team.
Another source of fan backlash is the hiring of the 4Kids voice actors after the death of Deem Bristow, the original Sega Eggman. Most people you ask about the voice acting on this game will tell you its the worst in history. These biased people can be ignored. While I will admit that the 4Kids actors have a real lack of emotion, I also have to admit that they aren't as bad as alot of people say. Granted, Jason Griffith's Sonic isn't exactly... Um... Good, but his Shadow is spot on. My biggest complaint is the scripting for the actors. The script for this game is parodied all the time in the Sonic community, and with good reason. There are so many examples I could provide of that, but my real problem is this.
D*MN.
Its EVERYWHERE. Whenever Shadow gets hit? D*MN. Whenever he falls? D*MN. When he's looking for that D*MN fourth Chaos Emerald? Self explanatory. Whats worse is that almost every character is given a nice little D-Bomb to drop. Knuckles? Yup. Sonic? Yep. Espio? D*MN right. Tails?!? Maybe. I've heard reports that even Tails drops a bomb in the Air Fleet level if the President's carrier is destroyed. I can't confirm this, though. I can confirm that Sega made a huge mistake when they decided to make their characters edgy like this.
On the other side of the sound spectrum, however, the soundtrack is one of the best of the 3D Sonic era. Senoue, Ohtani, and a host of others really did a bang up job. My only real complaint is that Jun relied too heavily on a synthesizer in alot of the tracks that didn't really need one. Of course, Jun has done this since his inception as the Sonic Music Master, so it wasn't exactly a surprise. Still, he needs to lay off the synth and just focus on giving us those classic riffs of his.
All in all, the game is nowhere near as bad as most would like to make you think. Its far from a classic, but its definitely worth a chance.