Hasn't seemed particularly lethal to me. I'm currently DMing one. We've reached about Chapter 8. I have a moderate-optimization party - two new players, three very experienced players - and I've had to consciously amp up the difficulty of almost all of the encounters to prevent them from chewing through the scenery. (This happened with a previous group as well - we cakewalked through the whole thing up to the last bad guy).

One big problem with the module is that half of it was designed for 3.0, and then migrated over to 3.5. Most of the standard optimization tricks are totally absent from even the mooks, let alone the lieutenants and main villains. Sounds to me like your DM is either playing the bad guys with extreme intelligence, or ramping up the difficulty.

What's your party composition, where are you at in the adventure, and which things have seemed particularly hard?