Just did the "Pepsi Challenge" between Iron Man (Dolby True HD) and Iron Man 2 (dts HDMA) and there is a CLEAR and obvious difference between the two. I always felt slightly underwhelmed by the battle scenes in IM but not so IM2. I was blown away by the bass and tonality of dts HDMA.
Saying that, I watched The Dark Knight on Sunday night and I was blown away by the audio. It felt like I was listening to dts HDMA. I put this down to my new receiver. (Onkyo HT-RC180).