- On YouTube itself, after 5.8 million views (in less than 12 hours!) there are nearly 120,000 likes and only 2,600 dislikes. That's 98% on the positive side. (I know this is biased because fans are more likely to be early viewers of the trailer, but that is still strikingly high!)
- To check with the Batman fans, I went to Batman-News, which has very active (and often critical) comment boards. I scrolled through more than 100 of the initial posts about the trailer and literally every single one was positive or neutral... 0 negative comments.
- To check with the Superman fans, I went to Superman Homepage, which has less active comment boards (and fans who are usually very hard to please, especially in the movie realm). Even here, looking at the first 75 posts on their comment board, there were 50+, more than two-thirds, that were positive. (Some of the negativity came from not everyone being sold on Lex, although I think he's sarcastic and disarmingly manipulative, or concern that Superman might be overshadowed by Batman.)
EDIT: I've now included above our analysis of the trailer. One thing to note is that some additional elements from the purported plot synopsis seem to be confirmed, but other things (e.g., the soldiers with the S-insignia) seem to be out of step with that synopsis.