1901-2000 World Coin Book. Opinions?

It is a good book to get, definitely. You can find many resources online to identify and give information on world coins (numista, worldcoingallery, etc.), but Krause's catalogue is fairly comprehensive and complete (although I guess occasionally someone on these forums points out one or two rare ones that they've missed, but they probably update that the next year).

I myself have the CD version that came with a pdf that is searchable, which made organising and identifying many of my coins much easier.

Not sure what you mean by "research", though. From what I remember, each entry on a country starts with a short intro on that country's coins, and then gives simply physical details of each coin, along with differences and a picture.

The Krause catalogs are pretty good and they are very comprehensive. They don't offer any assistance is trying to grade the coins for which they provide values for in various grades. Unless you have a good knowledge base of coin collecting where you could make a good guess as to grade just based on experience seeing many coins, this could be a minor issue.

I suppose it also depends on how much you already know about your coins. I once inherited a whole bunch of foreign coins. I couldn't understand what some of them had written and I had no idea what country they were from and the Krause catalog won't help you "find" a coin in that sense.

My only other complaint is that they just have so many pictures and values of all the "not intended for circulation" coinage that so many countries have issued during the last 20 years that it takes up way too much space. Some obscure countries have put out 4-5 novelty pieces per year for the last 20 years and it takes up pages upon pages that almost nobody is ever gonna look up. It just irks me personally.