Well, as many of my readers/blog followers know, I think there are ways to square the tragic Shakespearean anti-villain in Thor with the (apparently) flamboyant sexy bad guy in The Avengers, and my longest ongoing work of fanfiction is an effort to do just that. Loki’s time in the Void definitely changed him; it hardened him in certain ways, but clearly he has also fallen under Thanos’s power in some way or other and remains vulnerable. His loyalty to his family and Asgard (though not Odin) was also recoverable, apparently, so whatever happened didn’t completely turn him evil.
Whedon was deliberately leaving open a possibility for redemption by showing Loki as under threat from Thanos, and not just violent and power-mad but fearful. He also showed that Loki was conflicted, and genuinely tempted by Thor’s offers of affection and salvation. Ultimately, I think Whedon came closer than anyone else to approximating the classical tone of the first Thor, though The Avengers was more epic than tragedy.