As a longtime Spider-Man comics fan, I liked it.
I think the first half was a bit sluggish. The trickiest part of doing a superhero movie is making their lives outside the costume interesting. Raimi tried and came damn close, but came up short.
The fight scenes were magnificient. This is how I always envisioned Spider-Man and Doctor Octopus battling one another. Could this have been accomplished ten years ago? Heck, no. It's only with the benefit of CGI that we don't have a battle scene that makes us laugh our socks off.
The humor was a bit flat in parts, and while I liked the J. Jonah Jameson character, I thought he was mostly overused.
Where do we go from here? Spoiler warning. I think Harry's poised to take the role of the Green Goblin, or Raimi might go a different way and create the Spider Slayer or Hobgoblin from the Harry character. (It's been done--remember when Lucas recycled the Death Star idea from Episode 4 into Episode 6?)
Don't rule out professor Dr. Connors (The Lizard) or little-known astronaut John Jameson (Werewolf-by-Night). Did you happen to catch that flying leap Jameson's boy made from the dock to the platform when he saw Mary Jane? Or the look on his face when MJ left him at the altar? That boy has another side to him. I also caught the passing reference to "Dr. Strange."
Villains I'd like to see: Kraven, Chameleon and the Vulture. But, please god, don't let this film descend into Batman's cycle of superstar guest roles as assistants or villains.