Firstly, each level will make up a whopping 2 gigabytes. That's about half a DVDs worth of storage...which is alot. Obviously, this is why it's on Blu-ray, but it may account for the current slow down at checkpoints and the like.
Also, due to the sheer detail and effects crammed down the Cell and RSXs proverbial throat, the game will run 30 fps, and will 'only' be at 720p. The detail is so high in fact, that the amount of polygons used in one soldiers face is roughly the amount used in one entire Killzone 1 level. As long as it doesn't cause any issues like the ones seen Madden '08, it should be fine.