Just a couple of points:

1) The 2 LOTR movies so far are among my favorite demo/testing disk. The both have great sound, and they are wonderful movies that can be watched over and over again (at least I can watch them over and over). And I can't wait for Return of the King on DVD!

2) I don't think the Helm's Deep explosion is inferior or necessarily superior to any other explosion in a movie. I think it it exactly what the engineers wanted. As Wayne pointed out, the Helm's Deep explosion is in a stone wall. They show the Urik Hia running in the culvert with the bombs. How thick was that wall? 10 feet? More? That is some serious stone work. This explosion basically happens under ground. My feeling is that it is very realistic and very dramatic. The guys who put that together knew what they were doing. You may disagree with their choice, but it was a choice, not an oversight or mistake. And, personally, I am not "underwhelmed" by it at all.

Just my opinion and my 2 cents . . . and worth as much, I'm sure