You know, muppetwriter; my best friend who saw it with me felt that the rushed feeling was due to character development. Harry's death was significant because we had three full movies to grow with and care about the character. While I really liked Topher as Eddie (and I mean that in a real way, I mean, Venom was a lot cooler with the mask pulled back to reveal Eddie's face), they flash him briefly on screen as a jerk and then kind of direct the film to make it seem in some way that we're supposed to feel sorry for him, like he's a victim. Then when he gets killed at the end, my initial thought was "Oh, that's convenient". But in truth, I think we should have gotten to know him more. Like you said, give more time to Flint Marko, he was a great character. Then use this movie to get to know Eddie and put Venom in a fourth movie. Then if you really want the two bad guys vs. Spidey, it's the perfect opportunity to turn Dr. Connors into the Lizard because we're nice and familiar with him now too!
Like I said though, I did like the movie, I will buy the DVD and watch it again, but the first two are still my favorite. They also had a similar rhythm. If you told me that someone other then Raimi directed this 3rd film, I would've believed you.