Can't say I agree with the sentiment of that letter.
Dr Who is a show that moves on, and, whilst we might hanker after a beloved era from the past, you have to remember that, had that era continued, we'd probably be bored of it by now.
Personally, I'm more than pleased with season 6 so far. I didn't think it started too strongly, but, since then, we've had a cast-iron classic in the shape of 'The Doctor's Wife', an enjoyable cloning two-parter. Hell, I even quite liked the pirate one.
And, based on last week's installment, Moff proves himself just as capable as RTD was in crafting a Bad Wolf/Utopia/Stolen Earth-style adrenaline-boosting cliffhanger, which helps make the show so genuinely exciting!
It's all good stuff and well on the way to beating RTD's fourth year as (IMHO) the best series to date. Another episode or two to the callibre of 'The Doctor's Wife' and it's there.
Regards,
Cypher