While I really liked the beginning of the edit with Hill at first, I kind of missed the original intro, and felt like this compromised the ending a bit, which in my opinion wasn't really seamless, especially when compared to the original.
Some of the added scenes were pretty great and IMO necessary additions, but some of them weren't really as great: The Hulk scene with the security guard would be great if not for the fact that it spoiled where Loki was going to open the portal to the audience, and I think finding it out with Stark really works wonderfully. Some of the added stuff in the battle is good too, but at the same time compromises the pace, like the bits with the guard and the chitauri gun (the audio and video of this part is also somewhat jarring). The additions with the waitress were great, though.
All in all I still preferred the original cut of the movie when putting the pros and cons of this edit. But that's just me. It's still a pretty good extended version of the movie.
First, let me comment on the skill of the fan-editor, samspider3: in a word, Excellent. The edits here are virtually seamless -- it was only my familiarity with the source material that clued me in to what was being added and changed. If you aren't familiar with the theatrical release, you would never guess what was changed (except for one scene, which was unfinished in the source).
Now as for the movie itself, I have less kind words. The Avengers as theatrically released is practically a perfect movie. Sometimes movies are cut for timing, sometimes because of studio meddling -- but sometimes scenes are cut out because they just don't work. An archetypical example of this is the Jabba the Hutt scene from Star Wars Episode IV: not only is it a clumsy scene in itself, but it simply restates the much better earlier Greedo scene -- and in the larger scope, completely spoils Jabba's arrival in Episode VI. It is better and rightfully left on the cutting room floor.
Just about all of the scenes added in Avengers EE are of this nature. While I love Maria Hill, she's just not a significant enough of a character to bookend the entire movie around. Scenes with The Waitress just stop the movie cold, especially during the Battle. An added scene with Loki and Hawkeye seriously spoils the later scene where Black Widow "interrogates" Loki. And is there any one person in the world who is finally satisfied knowing where Banner got the motorcycle from?
Even so, as a die-hard MCU fan, I would recommend this edit for an MCU fan's collection. I enjoy the Universe, and this EE allows me to spend 11 more minutes in the Universe, and for that I am grateful.
In closing, here's an idea I'd like to throw out there: Kevin Feige recently commented that they would not be doing any more One-Shots. It might be interesting (if possible) to take a bunch of deleted and other scenes and re-cut new One-Shots out of it. The Waitress, for example: make a little mini-movie with her as the main character. You'd even get a Stan Lee cameo in it. Other possibilities are out there, too. That would be fun to watch.
I watched this with a friend who is a very big MCU-fan, much bigger than I am. We came to the following conclusions together...
The new opening/closing structure is excellent; it makes the SHIELD element of the story, in particular Maria Hill, a much for valuable part of the overall experience. This will probably be the best version to watch if you intend to then get into Captain America II, for example.
There were a couple of bits that felt a bit out of place, most notably the cop who - during the New York battle - gets into the fighting with an alien gun. It starts well, but then ends rather suddenly and seems to go nowhere. I can see what the idea was here...but this late in the film it doesn't seem strictly necessary. The waitress, on the other hand, plays out very strongly in this edit.
Deleted scenes were occasionally noticeable by a dip in visual quality - this was most apparent when Bruce Banner wakes up in a crushed warehouse...here he has an extended discussion with a security guard that takes place in front of a very rough backdrop of New York. Again, the idea is solid, but this might be one to leave out.
Audio editing was top-notch, I didn't notice any errors.
Enjoyment was very solid - I never found myself bored, and the flow was maintained excellently even with a full 11-minutes extra. Sometimes an extended cut can drag a bit, but this played very well.
Would highly recommend that this replace anyone's go-to screening copy.