I got these for my son when he was 18-months and he LOVES these! He has already memorized both the First Words and almost all of the Shapes & Colors cards.
I went out and bought ALL FOUR packs. They are all great!
Each card includes a big color photograph of the item plus some sort of tactile addition - such as hair on the cat, bumpy tires on the tractor, sticky areas on the jelly. Plus, on the back of each card there are "talking points" and suggestions for questions to ask and things to do. It also has five different translations for the object, so you can help your little one learn other languages.
As other reviewers have mentioned, the cards are super strong and will resist bending and folding if your baby plays with them. My baby has at least once dumped them on the floor and danced on them - and they as good as new!
They are now part of our nightly routine. We "do cards" right before we read a book or two each night.
I would say that First Words are good for 12 mo+, and Shapes & Colors is good for 18+ (there are some more difficult cards, such as a picture of a glittery purse shaped like a heart - my son still has no idea what that is!). Animals is a little more advanced (just because it includes some more obscure animals) and Counting is the most advanced (but it is still awesome and teaches great concepts - for example, there is a picture of a jar of marbles and another card with an empty jar, so the baby can compare "many marbles" versus "no marbles").
Buy these! And, I hope the company makes even more of them (would love to see more themed word cards, such as "food," "bathtime," "bedtime," "outdoors," etc.) I will buy them all!