So Thanos is the next big bad. But why is Death's would be Romeo gagging to get at a backwater low tech world like earth anyway? What's his big prize?
Thanos is an Eternal. His people orginated from the Celestials seeding early humanity with the potential for great power. Thanos knows this and decided to test humanity to gage it's power and potential for violence.
Judging from his smirk he was most pleased. He wants to turn humanity into his army of death. He knows this is possible because at a basic level he himself is human. The Hulk alone probably made him giddy.
This is in contrast to Loki who looks down on humanity. Thanos would see the Avengers as the same as himself leading to greater pathos. Also the revelation that they every other race that has been seeded by the Celestials(Kree and SKrulls) have become galactic despots would cause some good moments.