The third edition is a major review of the Let's Go series. Much has changed, but much is the same. I'll focus on the changes.
* The art work has been entirely redrawn. There are no more 1950s TV sets. John and Lisa have been dropped
* The vocabulary has been greatly extended, there are probably about double the number of words, many of them from Let's go 2 or 3 (2nd edition). There are now 287 word cards in level one (up from 150).
* The teaching of verbs (in the Let's Move sections) has been changed. There are fewer classroom commands, but more verb grammar. The songs, Let's move and Let's talk have been combined into a single "Let's start" class.
* Some of the expressions have been simplified: from "Look, there's a bird. I like birds" to "What do you like? / I like birds."
* There are Let's build sections in each unit, which try to encourage vocabulary and pattern reuse.
* There is more review in the main units, and less in the review units The review units are replaced with a review listening exercise and section of extra vocabulary.
* Phonics are more extensively taught.
What is the same is the basic grammatical content and ordering.
This text will favour better students, but it will be very hard to effectively teach this text to weaker students in a 50 min per week, 40 weeks a year schedule. The content has expanded and students will need more time.