We've played with them a few ways, but we have found it is much more fun to turn it into a memory game, rather than just a simple matching activity.
We turn all of the picture cards face down in rows,
Then they have to try to find the matches for the letters they have, and remember where the pictures were if someone else flips one over.
When they find the match for the letters they have, they have to put the puzzle pieces together.
The first player to get the match for all their letter cards is the winner. This is one of those games that my three-year-old has really latched on to and wants to play every day. He just loves it.
You wouldn't have to go out and buy a set to play this game. It would be relatively easy to make your own version using google images from the web, and printing out the letters and pictures on your computer. Or, take pictures of things from around your home that begin with each letter and use those. It could be fun for the kids to see things they recognize. There are some easy options to try, and it is well worth it.