That. It is not an awful episode per se, especially if you see it as an homage to Indiana Jones. But it has no substance. There are random monsters, the thing they discovered is a one use thing which makes no sense, there is no explanation or discovery about what the thing was or its purpose. And it seems that nothing really matters. It is an episode you can skip without missing anything, or at least that is what appears to be the case so far.
Besides that, I think the season itself has a drop in quality, especially in the animation. I still like the music and the voices though. But I am not liking this season as much as the previous one.