The shield enemies took me a while to get used to. I finally started to get the hang of them. Or just saved all of my grenades for them.

Either or.
Now that I think about it, that bit on the plane took me probably fifteen tries. But I died so fast that it went by fairly quickly.
And I think there was one point in the boat, with the shield enemies, shotgun dudes and snipers, that took me quite a while.