Marvel's Avengers Assemble Season 2 Episode 13, "Thanos Triumphant" is a great prelude to the Marvel Cinematic Universe's introduction of Thanos

I sorta hated Avenger's Mightiest Heroes, since the animation was too low budget, with really bad fight scenes.

But this has really bad fight scenes too and the humor doesn't work, although it follows a logic. It tries to be blockbustery, and accomplishes a bit more than Joss Whedon does, despite no RDJ.

I find the acting in this to be very good. Some of the episodes seem rushed, but at least they state their expositionary goals correctly. Stop Thanos from gaining all the Infinity stones and conquering Earth, join together to fight him, 

The Guardians save the day.

Star Lord and Hawkeye are portrayed much younger than their film counterparts.

Ultron memories and child-like tone. 

It really failed cuz of the supposedly have to be cartoon cartoony action and Marvel humor, but really pulls it off in the serious dramatic parts of the episode.
It got me a sense of what Thanos can do.

I don't get how Captain America and Iron Man can survive most of those blows.

But it results in a challenge that makes the episode even more well crafted IMO.