Spiderman 3 is not that bad. Some people didn't find it satisfactory, but I found it perfectly likable.

Except maybe for that part when Peter Parker acts like he found the Mask rather than the venom gloop.

My favorite thing was how comic bookish Thomas Haden Church looked like regular (human not sand) Flint Marko.

I think that it felt about right for the source material. It's not like the Spiderman comic heritage is a logical, linear narrative.

The comic book movie sequence has to be something like:
Movie 1: origin story and fight a villain
Movie 2: fight a different (preferably cooler) villain OR fight 2 villains, expound on complications of superhero life
Movie 3: fight a bunch of different villains, and the stakes are higher

Of course, that's about as far as it can go and be decent. I hope they don't make Xmen 4 or Spiderman 4 with the current casts and crews, but they could redo either of them in a decade and I'd be fine with that.

If they make more movies within this sequence, it seems like they'll have to be worse. Where can they go... Resurrect old villains? Go to space? Go to another dimension? Time travel? Do a team up?

Really, the only thing that I think could even be somewhat decent as a movie is something like Fantastic 4 plus Spiderman. But that won't happen. And people wouldn't like it if it did.

Metacritic for the "mixed reviews".
official site
Spider-Man 3 is even christian approved.

Also: I'm happy they just called it Spiderman 3 without some silly subtitle.