Some people say that Thanos should not appear in, or only have an after credits scene in The Avengers. I say that Thanos should appear in the Avengers, and have a large role. He should not have the Infinity Gauntlet, for then he would be much too powerful for the team. I am saying these things because Loki would not make a good enough villain. If Thor can defeat him by beating him up a little, and then putting his hammer on Loki's chest, alone, then I think that adding Iron Man, Hawkeye, Black Widow, Captain America, and the freaking HULK to the picture, would make for a, with the cube, 5 minute final battle.. The Skrulls couldn't do much. They would really just be a thorn in the Avenger's side.I mean, Cap took out hundreds of Nazi's. With high-tech weaponry at their disposal. I think that just Loki would be to easy.
Enter Thanos. The Mad Titan. One of the most powerful characters in the Marvel Universe. Up against the most powerful team in the Marvel Universe (I want NO X-men comments). It would make for the most EPIC final boss battle yet. Say, 10 to 20 minutes of battling. The reason I say yet is because of possible sequels. Avengers 2 would give us Ant-man,Wasp,Black Panther, and the villain be Ultron. Hank Pym's rouge AI. Thanos would capture Thor and force him to tell how to get to Asgard. He would go while the Odinsleep is going on.He would enter the vault.
Enter the Infinity Gauntlet. Avengers 3. The Skrull-Kree war on Earth, with Thanos in the shadows. When the Avengers think it's over, worse things happen. Thanos could level New York in an instant, or have the Avengers die. He leaves the choice to the public. They know the two alien races will be back, and that only the Avengers can stop them. But, if New York is leveled, it would leave thousands homeless, and uncountable number of people dead.
Thanos would be amazing to see on screen. Yes, I loved Tom Hiddleston as Loki, but it would be too easy for the Avengers to beat him.