Some background, courtesy of Kerry Wilkinson:
Back during the Secret Wars, Spider-Man got himself what he thought was a new costume. It turned out to be an alien symbiote that wanted to possess his body. Spidey rejected it, however and it was left holed up in a church tower.
Shortly afterwards, Eddie Brock, a journalist with the Daily Globe lost his job after his Sin-Eater identity story was proved to be fake by Spider-Man. Wanting to end it all, he first went via a church to say his last goodbyes. His hatred of Spider-Man was picked up by the symbiote however and the two bonded to form Venom - a crazed killer who wanted nothing more than to kill Spider-Man.
In their many battles, Spider-Man triumphed consistently - even though his Spider-Sense doesn't pick up on Venom's presence. One time when Brock was in prison, however, the symbiote gave birth to another version of itself. This new symbiote bonded with Cletus Kasady - Brock's psychotic cellmate - and together the two became another crazed killer, Carnage.
When Carnage first escaped, Spidey teamed up with Venom and the Fantastic Four to save the city and re-incarcerate Kasady. Since then, Venom has re-escaped too and, after Spidey helped save Brock's ex-wife, formed an understanding with Spider-Man that he won't cause anymore trouble and that the two of them will stay out of each other's way. Most recently of all, in one of the best Spider-Man books of all - Spectacular 200 - JM DeMatteis scripted the death of Harry Osborn. He had gone crazy as the Green Goblin, wanting to blow up most of the city's leaders. After MJ and little Norman entered the building he was fighting Spider-Man in, however, he came to his senses, even saving Peter from the explosion, before he died in front of them.
Carnage, Shriek, Doppelganger, Demogoblin, and Carrion attack the heroes anew, and Morbius, Venom, and Cloak respond in kind. Soon, Spider-Man, Black Cat, and Firestar are also in the fray. Elsewhere, Mary Jane misses her husband, but we soon come back to the battle. Cloak loses to Shriek and retreats to regain his strength, evening out the numbers between heroes and villains. We then learn that Shriek has the ability to transmit her emotions to those around her, which is why the civilians are acting like psychopaths.
One of the psychopaths take down the Black Cat, which leads to Demogoblin beating Morbius. Firestar, Venom, and Spider-Man are busy fighting Carnage, and they decide to kill him if that's what it'll take to bring him down. However, neither Spider-Man or Firestar can deal with what they're about to do, and Carnage is spared. Venom is enraged by their actions, and Spider-Man has to stop him from killing Firestar. He knocks Spider-Man away.
While Venom bemoans the fact that it seems like stopping Carnage is up to him and him alone, Carnage and Shriek attack him. They make short work of Venom, and head off to torture him. Meanwhile, the rest of the heroes lay in defeat. However, another hero has come to aid them: Captain America.
Story-wise, this issue continues the trend in this crossover of having perfectly all-right storylines. Spider-Man and Firestar's brief crisis of conscience was a good bit, as was the end with Captian America suddenly showing up. Art-wise, however, it was a departure from the last issue. While the previous few entries into this crossover had clean, vibrant art, this issue looked rather blocky and flat.
Story-wise, it's perfectly adequate. Art-wise, that's where it gets brought down.