It's fairly leggy (but I've seen worse). Are you giving it plenty of light and not too warm? Don't let it get above 72 degrees during the day, and if you can, drop it down to 60-62 at night.

It's under a T5 grow light. None of the other plants are leggy. I wondered if it was just characteristic of the plant.

This is my first try with tomatillos, too, and mine started out a bit leggy as well. I potted them up, burying the stem as with tomatoes, and now they are happy as can be. I have kept the lights so low they almost touch since then and that seems to be helping as well.