We've gone once so far and we had a great time. It's easy to get to, has plenty of parking, and, best of all, is very interesting.
When we visited, there was a Modern Marvels from the History Channel show that they broadcast in the little theater. It was about 45 minutes long, and gave a great history of the Manhattan Project and nuclear science in general. It was worth watching before we went and explored the rest of the museum because we found we recognized names, locations, and dates from the show as we walked around.
The museum itself isn't huge, but it's laid out in a way that makes it easy to explore. There are interactive and kid-friendly areas scattered about and not one large kid area--great to hold their interest as you all walk through. The exhibits are labeled well and are often in chronological order, so you can follow nuclear history through...history.
There are special exhibitions as well, so check their website to see what's there.
I'd definitely go back, and I'd encourage anyone visiting Albuquerque to budget half a day or so to this fun museum.