Given what it is, I'd rather see it released as an expansion. I would be happy to buy more COD4 'episodes' and I suspect that's pretty much what it's going to be. $50 for more of the same wouldn't interest me a whole lot. Maybe if rather than the six or so hours of COD4 they gave you 20+ hours of the same quality it might be worth it.
It does seem like they're just breaking out the industrial milking rig.