I think I've been in the middle with every movie so far in the franchise, but things seem a little different this time around. While I think that Eclipse is a much better movie all around than the other two... mostly because the acting didn't make me cringe this time and David Slade did a magnificent job making the world of Twilight seem much more real and accessible than it has in the past... I was left feeling kind of empty.
It's a feeling I've noticed other people have in their 'middle of the road' reviews and though I'm not exactly sure where it comes from, someone did say in another thread that they think the movie would be much better if key scenes had ten to fifteen seconds added to them, maybe a pivotal line or two. I wholeheartedly agree. One of the things that has bothered me the most about the movies in the Twilight franchise is their running time. I don't understand why Summit seems to believe that all of these movies need to run at just above the two hour mark. If they haven't noticed by now, Twilight fans are not all underage tweens. Many of us are in our late teens, twenties, thirties, etc. and I'm pretty sure I can speak for even the little ones out there when I say that we're all more than willing to sit through a longer movie. I'm not sure if it's money or timing that cuts the films down to such a short running time, but I'm hoping that this trend does not continue with Breaking Dawn. Sure, it's being split up into two films, but that doesn't mean they should only run three hours total.
That being said, I did like the movie. There were many things that worked wonderfully for me, and others that unfortunately fell short. I'll break it down into pros and cons so I don't end up writing a novel of my own instead of a review. ^_^
Pros:**Acting- I thought that all three leads gave great performances and I was impressed with Jackson Rathbone's and Nikki Reed's flashback sections as well.
**Writing-I always enjoy the tongue in cheek humor that has been a hallmark of the series, but in Twilight and New Moon the rest of the movie was peppered with cringeworthy adaptations of SM's work. I was happy to see that this time (for the most part) the movie was well written.
**Action- The action sequences had some great choreography. The vampires seemed quick, graceful, and deadly and the wolves looked wonderful as well. I especially loved the tense scene where the Cullens are after Victoria and Emmett crosses the 'line'.
**Music- As always I am enamored by the soundtrack.
Cons:**Wigs- Kristen Stewart's wig was a pretty big distraction and though I don't know if it's a wig or not, I don't like Carlisle's pompadour. His hair looked much better in Twilight.
**Missing Lines/Scenes- I think I covered this when I said I didn't like how short the movie was, but I was really disappointed with some of the lines they took out. Jacob not referring to Edward as an 'eclipse', Edward not telling Bella he wanted her "Right now." etc... There were so many lines I kept waiting to hear that didn't make it in or were changed too much.
**Out of Character Behavior- This one has been covered by many of you already and I want to just reiterate how wrong it was for Bella to just leave Edward standing there in the school parking lot like an idiot. She may not have been my favorite person in Eclipse, but she knew enough not to do that. It's one thing if MR wants to make Bella seem more confident, but making her seem dismissive and resentful of the man she supposedly wants to spend eternity with makes her agreeing to marry him in end seem confusing.
Jacob was also not enough of a little punk and Edward needed to seem like less of a doormat. I mean, we're supposed to want her to end up with him, right?

*sighs* I really wanted to love this movie, but I've only seen it once and I'm hoping that it was my being tired at the midnight showing that prevented me from falling into the 'I loved Eclipse' camp. I guess we'll have to see after I watch it again.