I think I'm going to make it my rule from now on - no more buying Lego kits for M. Sure, there are some awesome kits out there and we do have quite a few at home. But so far playing with kits has been way too frustrating and not nearly as rewarding as playing with loose bricks.
I recently ordered bulk Lego bricks from Ebay. To supplement those I just bought an inexpensive (as far as anything Lego goes) set of 600 bricks (if you're interested, it's set #4628). With these two new acquisitions, M's been building stuff every day.
When it comes to kits, even fairly simple ones, he gets put off by directions. Even though he can follow directions reasonably well, he gets intimidated and requires too much hand-holding. With loose Legos he just builds, frequently early in the morning when I'm still asleep.
Not to mention that loose bricks let him build just about anything he imagines. Lately he's been building a rocket with a launch pad, a police station with a prison (after watching Lego Police episodes on YouTube), a truck to move "everything in the world", a bunch of satellites, a super cell phone and much more.
I still have to find or re-order the missing pieces. And I still have to come with a way to store the kits so they are accessible, but manageable. But hopefully M's building activities will be a bit less taxing on my obsessive-compulsive idea of "a place for everything and everything in its place".