Personally it just sounds like the writer of the email has worked very, very hard on a ride that took years to produce only to hear negative reviews. Of course they're going to take it personally. Imagine creating something you put your heart into for years only to have it slammed...it would be heart breaking.
On the other note, that same imagineer will feel better once s/he sees the countless families who'll wait 2 hours to ride the ride TSM and see the children screaming for their fav character. Heck, they should even be happy to see the positive reviews on youtube for the Mr. Potato Head AA. It blew me away seeing the footage, let alone experience it in reality.
While I have slammed a few rides in my day on WDW (Drew Carey, Stitch), the majority of new rides are unbelievably good (Soarin, EE, Dinosaur, etc.) and are in true Disney fashion. I know I can't wait to experience this ride and am glad that they're sprucing up this park.