It can be a tough one, although really only on Hard. Black Ops is a breeze (just shoot anything that moves or blows up with a grenade) and Easy/Normal both have more than enough Health Packs. Little trick I found was to deal with the entire final room from within the tunnel that leads to it. With some good shooting and a little luck you can finish it off without even leaving the tunnel, thus giving you a safe place to run away to if needed, since the baddies don't follow you up those stairs.
As for the lack of a boss fight, that was because the boss was being saved for a possible Black 2 as far as I know. If/when that game ever hits the market is anyone's guess, but hopefully sooner rather than later. And it better have multiplayer, heh.
--- "Have you seen the posts around this board. You HAVE to act like a child to get attention around here." - AlabamaMan79