It was out first official LA curriculum that we've ever used. We've read books about parts of speech like The Word Spy & really enjoyed every minute of our time with the books. In fact, my boys recently reminisced that they hoped the Word Spy was off on another adventure collecting more information to write a third book.
As for the WP LA, I've really enjoyed using it with the kids & watching them learn as they move along solving mysteries. Level 4 is not the only series in which there is a mystery to solve, Level 6 has a space themed mystery too, where as Levels 3 & 5 visit with Scout The Dog who is also a very loveable character to get to know.
My only word of warning is not to make a quick purchase without checking through the samples & considering looking over the Placement Test. Having not had previous experience this was a non-issue for me, but I've heard from others who've made the switch & ended up ahead of where their child was academically. Also, be aware that if you purchase Level 6 there is only very moderate instruction as the level was written under the premise that your student would have been learning all the information for the past 3 levels & is now ready to put it all to use.
For links to the placement tests & a few more details check out our review over on The Curriculum Choice.