I think people put way too much stock into an E3 presentation. I've bought, probably, 2000 games in my lifetime? Just a quick guess- that's probably way off. But I'm sure I've seen E3 footage for about 12 of them prior to buying it, and in zero cases did it make a difference in my decision to purchase. The only people who are upset about the E3 demos are people who are upset about the E3 demos, and they're upset about it because they're upset about it. It's like a self-contained cloud of emotions. That and it's easy fodder, both for haters looking to justify that hate by fixating on this one little thing, and by non-haters, to point to how almost none of the footage we've seen accurately represents the game yet.
Interesting that there will be options, though. I have to wonder if that is as simple as having these pre-built environment kills vs attacking though a meat sponge. I would hope it's a bit more than that. I was a little ore comfortable with the notion that I had in my head where the big epic fights vs. giants would be setpiece battles while the real, normal size bosses are traditional boss battles.