I think it would be nice if there was a better way of creating new entities, or perhaps specifically when setting fields in entities. I believe entity_js is setting the fields in a traditional way e.g.:

values = {
    "name": "username", 
    "mail": "username@example.com",
    "field_test": {
        "und": {
            "2": {
                "value": "foo"
            }
        }
    }
}

Would be nice if it was like:

values = {
    "name": "username", 
    "mail": "username@example.com",
    "field_test": ['foo', 'bar', 'baz'],
}

Not yet sure how to do this but I'm currently experimenting with EntityDrupalWrapper and I think this is be doable. Will try to provide a patch when I get around this.