Had this a few days now and have started to get into it big time. The difficulty is alot higher than the first one and some of the DX9 effects / textures look fantastic.
Its the same as the 1st one overall with a new story, but on this one you get to kill alot more people. Only a few of the levels so far you arnt allowed to kill anyone and on those levels nearing the end the no kill gets revoked so you can just go for it. They seem to have incoporated quite a few more action bits in it (Like the end of the first one)
Definately well worth getting.