Well, I won't endorse a letter praising a game to a man who is not a gamer, and other than strategic direction, probably had nothing to do with the game that's actually in yours and my hands.
However, I would write the following letter:
Dear Mr. Rouse and all gamers who work for WotC and were instrumental in the creation of 4E:
As a long time gamer and devoted fan of D&D, I wanted to write you concerning the game and the direction it has been going in. I am certain you have recently received a number of letters expressing dislike at the new path 4e is blazing, and in the general direction which the company is heading in. In light of that, I'd like to say that the direction of the company is not your fault. And, even though I don't play 4E as my preferred edition, all of you have created a wonderful game that has brought many new players into our hobby, and made many long time gamers re-invested in the hobby. Even though, as a whole, I prefer 3E, there are a lot of things in 4e which are sheer genius. And, the ongoing ideas and settings coming out of R&D are as rich and enjoyable as at any other time in the history of D&D. Job well done, and keep up the good work.
Whether 3E, 4E, or any other edition or game, I would greatly enjoy gaming with any of you if I ever have the good fortune of someday crossing paths.
Hang in there and, GAME ON!
Sincerely,
Mark "El Mahdi" Armstrong
Devoted "Gamer" (not devoted "Customer") since 1994