Well, I honestly think the CGI is bad. It's way too obvious and cartoony. The texturing is truly, truly awful. Most effects does not equal good effects.
. That was perfectly and subtly executed.
As for Avengers, they were merely OK, middle of the road Marvel film effects. Nothing too exciting. Though I do remember laughing at the poor quality of that fight scene between Thor and his brother in the middle of a storm or whatever that was.
There were some moments during The Avengers when I felt the effects during a certain sequence looked really good (pretty much the whole Helicarrier segment, Iron Man in general, the opening sequences) while sometimes they looked downright bad (Thor fighting his brother, some of the final battle, the space stuff with Loki). I think the main issue is the consistency with the effects. At times they look really stunning, but there's not a 20 minute stretch where there isn't something that looks a little iffy.
They were really good, but because of that I prefer the effects of even TDKR, where basically there wasn't a moment that stuck out as poor.