Not scriptural. Able gave the FIRST; right off the top, not the best.
He spoke of how God says that Abel still speaks even though his blood ran spilled upon the ground, indicating that while Abel is dead, yet he lives.
I remember not being able to figure out just why God was displeased with Cain's sacrifice as the text doesn't really indicate. The only thing I remember sensing from the text is that Cain's sacrifice seems forced.
Our Pastor did elaborate on this, and what I came away with is that Cain's sacrifice seems to have been made more from a motivation of obligation that devotion, and Abel's was just the opposite. Abel's sacrifice was made with Faith, first and foremost, then devotion and humility.
I think your additional points about anger are interesting. Also, I love the Pyromaniacs blog (the artwork is really good), along with those he links to, and Real Clear Theology (we do the theology for you......so you won't hurt yourself). Though that blog doesn't have a whole lot of activity as of late.
There are a lot of really great Protestant blogs out there. I'm not sure which link provided by Pyro I clicked on (maybe Frank Turk?), but it lead me to a blog called the Black Calvinist, which was good, and also to a UK blog, which had a great sermon on God's gift of human sexuality.