This is very overblown, the first mission is fun.
Yes, you can hide behind your allies and let them do all of the work on that mission because they were made indestructible. That's a lot better than them getting clipped by a stray round and you failing the mission, and why would you want to hide exactly?
A thread like this is like saying that UT'99 sucked because you could join a Face server and piston camp the top portal and get kills without doing anything. If you got bored doing that, it was your own fault for being boring. Games are fun (or not) based on how you interact with them, and I had a lot of fun playing through Black Ops singleplayer aggressively.
Yes you can play aggressive and pretend there is a challenge, however you are the equivalent of a child with a wooden sword pretending he is slaying dragons in his backyard. This game uses imagination to simulate challenge and risk that aren't really there. Of specific note: there is a sequence where he runs and gets shot a bunch and states "these bullets can't really kill you", then there is the mortar explosions that he runs directly through for 0 damage, then there is the plane sequence where he never even fires back.
The point here is that there is a fine line between "scripted sequences" / "AI assistance" and complete and total broken invulnerability. This game does not present you with any sort of challenge. He wasn't playing on "Very Easy", he was playing on "Hardened". Which is supposed to assume the player has some semblance of skill and would like to be challenged in some fashion.
Now since I haven't played the game (and not sure I ever will), I can't say how the other levels compare to this supposed "tutorial" level. But I will say that if the player chooses "Hardened" the game should not coddle him in a tutorial in such a ridiculous fashion. This may be the developers only mistake, but it is a pretty large one.