The big break from many philosophers, I think, is considering preferences the foundation of ethics.
No, this is called preference utilitarianism.
(...) and the most controversial around here I think, is that Eliezer thinks that human preferences are similar enough across humans that it makes sense to think about should_human.
Not only controversial here. Even when just being the messenger, during discussions on morality, I usually get called out on that. The hope on ev-psy as argument for very common values plus the expectation that value differences are more often differences in knowledge than differences in culture or subjective preferences is not shared very widely.
No, this is called preference utilitarianism.
Usually utilitarianism means maximize the utility of all people/agents/beings of moral worth (average or sum depending on the flavor of utilitarianism). Eliezer's metaethics says only maximize your own utility. There is a clear distinction.
Edit: but you are correct about considering preferences the foundation of ethics. I should have been more clear
In You Provably Can't Trust Yourself, Eliezer tried to figured out why his audience didn't understand his meta-ethics sequence even after they had followed him through philosophy of language and quantum physics. Meta-ethics is my specialty, and I can't figure out what Eliezer's meta-ethical position is. And at least at this point, professionals like Robin Hanson and Toby Ord couldn't figure it out, either.
Part of the problem is that because Eliezer has gotten little value from professional philosophy, he writes about morality in a highly idiosyncratic way, using terms that would require reading hundreds of posts to understand. I might understand Eliezer's meta-ethics better if he would just cough up his positions on standard meta-ethical debates like cognitivism, motivation, the sources of normativity, moral epistemology, and so on. Nick Beckstead recently told me he thinks Eliezer's meta-ethical views are similar to those of Michael Smith, but I'm not seeing it.
If you think you can help me (and others) understand Eliezer's meta-ethical theory, please leave a comment!
Update: This comment by Richard Chappell made sense of Eliezer's meta-ethics for me.