Both reviews were well done, both gave sound reasons for thier opinions which made sense, and honestly in my opinion they were right about most of it.
Show me where exactly they were wrong?
Were they wrong about having relatively low player content compared to what was advertized on the back? No there isn't a plethora of new player content.
Does the book have too little pages to justify being a hard cover? Yes, its doesn't open right or stay open, which reduces the quality of product.
Most of the rest is subjective, but they explain they're opinions. That's more then most lf the good reviews its gotten on this site do, and honestly I think the net positive review its gotten is underserved.
I agree with iO9 and escapist it tries to do too much and succeeds at none of them, for which I blame WotC for not the authors, its good enough to show you hint at what it could have been.
Let's unpack the iO9 review shall we?
iO9 Review said:
The Sword Coast Adventurer’s Guide is especially disappointing. It’s really the first book Wizards has released for fifth edition D&D that isn’t a dreadfully long hardcover adventure campaign, but if you were hoping for a some quality splatbooks to expand your D&D campaign, you’ll have to keep waiting. The back cover copy claims it’s a “valuable resource for Dungeon Masters and players alike... contains a plethora of new character options.” None of those things are true unless you define plethora very loosely. It’s about 150 pages long and feels a little on the thin side for $40.
The first 120 or so pages offer a tour of the Forgotten Realms and describe how the various D&D races fit within that world. There isn’t a single game rule or statistic to be found, which might be fine if this didn’t feel like a reprint. The Realms have been described and redescribed in every edition over and over again—I doubt there’s anything here you couldn’t find in a wiki. There’s a nice map of the Sword Coast region, where we’ve been playing video games and introductory adventures for almost 20 years, but it’s a single page, not a foldout. Can we visit somewhere else in the Realms for a while?
The final 30 pages or so are decent, offering new class options specific to the Forgotten Realms and some useful flavor, like new wizard groups to join, new deities to worship, and several new backgrounds. If this section was the gravy on an otherwise useful book, it would be perfect, but here it takes center stage, and this content just isn’t strong enough to make the book worth your time
Ok, he complains the books is a "little on the thin side for $40". Fair enough. And certainly a valid criticism. Is it the value for the money? Of course, that's not what people are talking about in this or the other thread, so, that's more or less up to the reader to decide.
His next point "if you were hoping for a some quality splatbook" is a serious misstep. WotC made no secret that they were not going to make splat books. They've been saying the same thing over and over again for the past year. If you bought this hoping for a splat book, then that's on you. This was never supposed to be a splat. This is a setting guide for players. It does say that in the title right? I've read more than a few player's guides over the years, and I would never expect a player's guide to not be 75% flavour. I've got a Player's Guide to Thule sitting right here and, yup, same thing. I've got a player's guide to Zeitgeist, and yup, same thing. I've got a players guide to Scarred Lands on my shelf, and, shock and surprise, it's exactly the same thing.
Why is this a shock?
Now, his complaint is that the flavour material feels like a reprint. That it's not visiting "somewhere else in the Realms for a while". Well... it does say where it's talking about right there on the cover. It's not a guide to Faerun, nor is it anything other than what it is - a guide to the Sword Coast. Why would you expect this book to cover anything outside of the Sword Coast in anything more than a couple of paragraphs? Sure, be disappointed that it's not covering a different area, fair enough, but, that doesn't make this a bad book. Complaining that your Chinese restaurant doesn't have curry is a bit on you, not the restaurant.
And, in the last paragraph, he's pretty much showing his own preferences - crunch over fluff. Fair enough, reviewers don't have to be even handed. I'm a huge Jeremy Clarkson (of Top Gear) fan, even knowing he's a giant ass sometimes. Fair enough. But, again, a book isn't bad because it's mostly flavour. He's disappointed in the book because it's not a crunch heavy splat. Well, again, fair enough. But, since WotC's flat out said, multiple times, that they aren't going to produce crunch heavy splats, well, he's going to be disappointed by pretty much every book that comes out. He says the book is poor value because it doesn't have enough crunch and he doesn't value the flavour material because it's talking about an area of the Realms he doesn't care for.
Well, sure. This book is not for this dude. That doesn't make it a bad book, nor is this review particularly scathing really. He discounts flavour text as being for players. If you're going to quibble about the copy text on the back cover, good grief, that's just par for the course. Of course, what is a "plethora". Six full classes? They've just increased the number of classes in D&D by about a 15%. That's not exactly small potatoes. Since he actually thinks that the class section is quite strong, just how much class material would you expect in a book like this?