I happen to still think its a very good movie but that's incidental. When I said what you quoted I was referring to this forum generally. Everyone (apart from the cool people) was giving it 10/10. I'm sure you remember.
Gonna go ahead and drop my two cents on the counter here.
Avengers is a one-time watch (and it took me getting dragged by my friends to see it twice to realize that). It's a mostly-hollow fan service session that lacks proper dramatic meat. People were so excited to see the Hulk smacking Thor that they forgot what makes a good movie. For a time, Avengers was so hot it was infallible, even though it felt like it was made only to justify the existence of the previous films.
In terms of character arcs and drama, the movie fell flat -- save for the scene where Banner admits to his suicide attempt. But even that was too little too late. The thing was all flash and no substance, which I suppose makes sense because the characters had already been introduced and we were expecting them to just team up and fight. In that respect, I hope Age of Ultron delivers more drama to counteract the bloated flash and self-awareness.
Guardians had infinitely more depth and creativity. It felt much more involving as an action/adventure film and I gave a damn for reasons other than seeing Hulk punch a giant space worm in the face. Okay, cool. Spectacle is why we came, but now give us something to stay and sit for. Tony being a lovable ass? Thor having a god complex? Loki being an unexplainable panty-dropper? We can get plenty of that by watching the other movies so why should we care what happens to the characters and their world in this one? A new reason, please. With substance. Otherwise it's just, as I said, a two-hour fan service session and nothing more.
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