At 5:00 tonight, I finished work on the playhouse. Here's the finished product:

I wanted to add a huge chalkboard along one side of the sandbox, monkey bars underneath it, and a bench inside it, but I've decided to save those features for future summers. I figure that if I add a new trinket or toy to the playhouse each year, maybe the kids will stay interested in it for longer.
Also, Suzy was worried that if I put a bench in the playhouse, kids would stand on it, lose their balance, fall over the railings, and plunge to their deaths. So instead, we've decided to stock the playhouse with a couple of outdoor beanbag chairs. They're more comfortable and a lot harder to get a good push off of if you happen to be a suicidal four year old.
I also added a tube that goes from the top platform down to the sandbox below. Here's what that looks like on the inside:

Yes, that is a toilet flange, but if any little kid ever uses that toilet flange as a toilet flange is typically used, that child will die. Here's what the tube looks like from below:

The kids have already spent hours pulling buckets of sand up in the pulley and dumping it all back down the tube. Suzy especially loves this tube, probably even more than the kids.
All in all, this has been a good project for me. During my time off, I tend to get on Suzy's nerves if I don't keep myself busy. When I retire in 30 years, I'm sure I'll drive her absolutely nuts. This project has kept me out of her hair. It's done now, and classes don't start up for another 24 days, so I'm sure I'll be poking around the house, driving Suzy batty in no time at all. Wish her luck.