Like many fans of the show, I believe that Thomas & Friends has been going down a slippery slope over the past few years in terms of writing. However, this special marks the debut of a new head writer, as well as new animators in the form of Arc Productions ("Gnomeo and Juliet" and "9"). So, does it do better than the last few specials. Definitely!
The main characters that many fans know and love are in character throughout the special, and this leads to some rather funny and witty lines. Also, the new characters introduced in this special are, for the most part, well written and developed (one character's back story even tells a history lesson about the early days of the railways). It's safe to say that writer Andrew Brenner did his research well, as there are a few references to the classic series included, and the first few minutes touch upon something never shown in the TV series before.
The animation by Arc is bright, colourful and fast, but there are a few points where it feels a bit unfinished. However, for a first attempt, they did very well, but I don't think I like the animation as much as that by Nitrogen Studios just yet.
Fun, knowledgeable, and just all around good entertainment, King of the Railway is a good watch for all fans of the little blue tank engine. Welcome back, Thomas!