I've heard nothing but admiration for him; from what I've seen, he's pretty much the godfather of Shadowrun, the ivory tower of which everything after is a mere shadow. Which book should I start on if I want to get a feel for what everyone wants the Shadowrun world be be like?

If you mean source material, I'd recommend the Denver Boxed Set. That is, if you can find a copy. I always thought the beauty of this was the GM selectable difficulty options for the NPCs in the GMs book.

If you mean novels, then 2XS is definitely the way to go.

no question, 2XS.

One of, if not the best shadowrun novel. For a low level runner who suddenly finds himself working with the A class runners it is great.

The Aztlan Sourcebook. The Shadowrun novels are pretty much all useless in nearly everyway, except to glean some precious details from.

Every book he wrote.

The candle that burned twice as bright burned half as long.

That means Kenson will live till 200 and mfb will live forever.

(mfb was just a random target)

So has the world, like, not developed much since Nigel died? It seems as if a lot of the later books do not add nearly as much novelty to the world as Findley's invention of Thomas Roxborough and the like did.

The world has indeed developed. That is the part that I have a problem with. instead of having a static world with information source books we have these ever twisting metaplots which affect the whole world, instead of stand alone. I like how DnD for instance, will have a party perform heroic and epic adventures, yet the whole social structure of the planet is not affected. There are no parallels and tie ins necessary.
Also if you want to have oriental adventures, you buy a supplement that doesn't change the whole world.

I went back looking at timeless and book credits, I think the development has shifted focus, and lost its grittiness and development edge after Nigel died and Tom left. You can see several patterns with plots, source books and quality with each line developer change. I find there is no specific point which you can nail everything down as all the transitions were gradual.

I think personally, that Nigel just had a huge amount of talent. Tom was with shadowrun from the beginning (at least that I can see) and did a great job in carrying through that flavour. With each hand off, the flavour and style changed, but it was kind of gradual because the people involved started subtly by writing minor parts then becoming more and more involved.

2XS hands down. You'll also want to check out the sequel House of the Sun. Burning Bright is also one of the best books and was written by Tom Dowd. Can't go wrong with any of those three...I've read them all many times over the years.