Can anyone clear up how much the initial game is, and then how much the packs are? Because I actually don't think it's a bad idea. I mean, there are many many games that I've bought in my gaming history for full price, that I played for a few levels, realised it was crap, and then wished I only spent a third of the price on it.
So it's all down to the price in my opinion. As long as they are offering the original game for a small amount, and then the packs for even smaller amounts. I think it's a good idea in the long run.
However, I can see some negatives. If developers don't bother creating the extra content unless people are coughing up the cash (in other words, only if the game becomes popular), then there could quite possibly be a stifling of original content. There are many games I've beaten and loved that no one else has even heard of. If developers don't bother finishing a game because no one's buying the packs, we have a problem.