Avengers Assemble #20 an Infinity tie-in? Says so on the cover, but it's not in the least bit just like a majority of the non-Avengers tie-in issues.
For some odd reason, Marvel chose to go in a different route regarding their Infinity tie-in issues that aren't Hickman Avengers books. While Hickman's books provided us with great art and content related to Infinity, the other tie-ins have been pretty much horrible. Marvel missed a big-time oppurtunity to give us some really cool stories featuring the Earth's heroes taking on Thanos' army. Instead, we have been getting issues that really have nothing to do with the main event or even the book the story takes place. The latest tie-ins have been more centered around Fraction's upcoming Inhumans event, and if these are any indication as to how that is going to go - good luck Matt Fraction (and you are going to need it after the disaster called Fear Itself).
Al Ewing provides a rather bland story about one of the new Inhumans who happens to be able to maniplulate size. Enter Wasp, Wonder Man and Scarlet Witch as we learn some mumbo jumbo about this and that - that no one really cares about. The story in itself is dull and boring, and I found myself at times not even reading the dialogue as it just wasn't interesting. Likewise, the art wasn't the best either as I found the artist using the same drawings over and over (possibly he was on a tight deadline, I don't know).
Overall, this is just another issue that says it's Infinity - but it's not - that can be skipped in its entirety.