I thought sPidey 3, like Hulk, was what I call a bad "good movie". It had everything the fans loved but too damn much of what critics believe these films need. That said, I disagree that Venom shouldn't have been in this film. Sandman was the odd villain out. Harry's arc came into full fruition in this movie and Peter's dark side was explored in flipside of sPidey 2; Then, he wanted sPider-Man out of his life and now he wanted more sPider-Man in his life. And the black suit, the sPlit personality, the evolution of his most personal villain was all a perfect metaphore.
But then they threw Sandy in there, turned him into a really nice guy who just accidentally shot Uncle Ben in what was the most groanworthy retcon since Underworld Evolution rewrote the first films entire history.
^I think they got it just about right.