I saw DEH at the final Broadway preview, and I thought Platt was spectacular (which does not mean he is not replaceable). He really left it all out there, particularly in the school assembly scene where "You Will Be Found" is done. But I saw the show twice more in the next several months, and, as is often true, it was not the same. He was very, very good, but not at the same intensity as the first time, or maybe I was trying to recapture something that is not recapture-able in live theater. But I think part of it was a difference in intensity; Evan was so lonely, desperate, and needy the first time that it seemed that his deception was more forgiveable.
Probably the most heart-breaking part of the show for me that first time was in "For Forever," when Evan sings about how he was lying on the ground after he fell from the tree, but fortunately Conor was there to help him. Platt's desperate desire for that vision to have been true was not there at the same level on the later visits.