This is one of my daughter's favorite books! We have three from this series and I would rank them:
1) My First Words (this book)
2) Tabbed Board Books: My First Farm: Let's Get Working! (TAB BOARD BOOKS)
3) My First Animals: Let's Squeak and Squawk (My First: Animals) (TAB BOARD BOOKS) (This I think will be excellent for slightly older kids, maybe 2+. As much as my daughter loves animals and they have been a number of her first words, the Animals book is quite a bit more advanced - if you're looking for a book for a 1 year old go with the First Words or Farm book)
My daughter is 14 months now and we gave her My First Words for her 1st birthday. It has been perfect as she's been learning a ton of new words recently, and I think it will easily hold her attention at least through the next year as she continues to discover new things. We gave it to her because she had the My First Farm book from about 10 months and it's also one of her favorites.
It is the first thing I grab for long car rides because we can spend a long time reading it.
Some of the tabs correlate to other books in the series, which can be a pro or con depending on how many of the books you have. Everything on the farm page is in the Farm book, which is slightly redundant, but it's also nice to see which pages she likes and then we will probably buy the corresponding books when she gets older. (And she doesn't mind redundant... it's good for learning anyway.) We already bought the Animals book because she loves the Wild Animals page so much, and I would say that book is quite a bit more advanced. I think the Things that Go book would also be a nice compliment for a kid that likes that page, and we will probably buy it eventually as well. But I guess the reason we like this one so much is because it has the highlights of the other books plus other daily/common things and activities. I also think this helps my daughter see what kinds of things go together too, since the tabs/pages are by category, as opposed to books with just animals or just colors etc... From looking at the previews, I would guess this book would be the most redundant to the Busy Day book.
I substitute our own words sometimes, for example I've been calling the "cup & saucer" on the household page a "mug" because that's what we have at home (and it looks like a mug). But that's not a criticism of the book - just that some people call things different names. There aren't a lot of these, none-2 on each page.
My only criticisms: 1) the food on the food & drink page seems kind of random to me. Not that it's bad, I have to imagine there were some difficult decisions involved to reduce the world of foods to one page, but you'd think they would include more foods more common for toddlers (cupcakes is the most random to me). It is a mix of healthy (various fruits and veggies, salad, sandwich, milk, etc.) and unhealthy foods (cupcakes, ice cream sundae, potato chips, chocolate) - this is fine with me but some would probably prefer just the healthy foods. The only drinks are juice and milk (in a jug, not a bottle, which I know is important to some people). 2) Likewise I'm not sure why they don't just have a "shirt" or "pants" on the Clothes & Shoes page. I just say pants for the jeans and shirt for the t-shirt, or say "jeans, which are a kind of pants" (my daughter loves the word "pants" but doesn't wear jeans very often)
We gave this to a friend who is using a lot of sign language with her baby, and she said it has been great for practicing signs. (We have done some of this too.)
The tabs are:
All About Me - on the left side it points out parts of the body and face, and shows 4 facial expressions; on the right side it shows actions (walking, sitting, etc.)
Clothes and Shoes - four different kinds of shoes, some cold weather wear (hat, mittens, scarf, fleece), pajamas, underwear, and then your basics
Around the House - about half are kitchen things; note there is no crib, which is probably good for co-sleeping families or kids who are already in beds
Food and Drink - see comment above
Pets - goldfish, puppies and dog, cat and kittens, pony, etc.
Playtime - these are all toys
Things that Go - train, car, bus, etc.
At the Park - nature items, animals, and activities
At the Beach - beach toys, swimsuit, sun block, beach towels, popsicles, crab, seagull, etc.
On the Farm - mostly animals, a tractor, bucket, wheat, eggs
In the Wild - all animals, quite a variety
Colors and Shapes - 1-2 pictures for each color (e.g. an apple and leaves for green, a banana and buttons for yellow, rabbits for white), and 8 shapes across the bottom of the page
Numbers - Zero through 10, with pictures to count with each number.
Every page has some action in addition to naming each picture, e.g. "which toys might make a noise?" "let's stand tall as a tree!" and "What do you like best about the beach?" - we don't do these yet but but I think they are what will continue to make this book interesting as my daughter gets older.
The book is pretty durable. My daughter has bent the covers on a lot of her board books (the ones we let her play with anyway) and the only injury to this book is she's folded up the car tab (which is the weakest, as the top right corner tab); I will probably fix it with packing tape, but it's only noticeable from the back of that page. I have rescued it from her sitting on it folded backwards a few times and you can't even tell. She pages through it quite easily by herself.
Lastly I'd like to say how much I appreciate the neutrality of this book. It's not overly "cutesy," has a nice mix of colors (not just kid colors) on white backgrounds, so while there is a lot on each page I find it very pleasant to look at. There's hardly anything that is girl/boy specific, even the doll on the toys page is not overtly girly (although it is a girl). I don't know why, but the Around the House page feels very Ikea to me.
I personally loved DK books growing up. I don't think you can go wrong with them!