The biggest complaint I ever hear about Bella is that she's too weak as a character. She allows her love for Edward to completely take over her life. She relies on him and can't function when he's away from her. Additionally, she's weak physically. She's described as a small person who can easily be overpowered by humans, let alone vampires. For this reason, she rarely fights back for anything that happens to her (what's the point?).
I'm actually going to argue this one a little. I think Bella is extremely strong-willed. Yes, you may disagree with what she's fighting for (to be indefinitely connected to Edward), but it is something she fights for. She's determined to get what she wants and won't be easily swayed by others. And, let's get real here, it would be kind of pointless for her to fight back against vampires. She's entirely too human.
Now, my rebellious let's-say-something-nice-about-Bella-because-I-still-kinda-like-her stuff aside, she does fall on the weak end of the scale. I would have preferred if she was a bit stronger and I think her likability would have improved greatly if she was. Sure, I wouldn't expect her to be physically very strong, especially against vampires, but isn't she really smart? The book implies that she is. If so, why isn't she portrayed as a great strategist or something? Having that extra element would have made her more interesting and shown off how she could be an asset to the Cullen Coven.
So, what do you think? Is Bella fine as is? Needs a strengthening make-over? Or (heaven forbid) should she have come across as weaker?