I hadn't even realized the shield-guys were vulnerable at all. I did get past that part, and up to the boss. (Wow that's a lot of health!) The more I play, the more interesting I find the "hovering"; like, you can't jump far enough to jump over a monster, but you can jump and hover to let it pass under you.
The other interesting thing is, the way the game plays, it seems to encourage you to move slowly, pull one or two enemies at a time, basically be cautious. I don't know if that was intended or merely emergent. ;)