Great place- if you have kids, the kid's area on top of the parking garage is both a great use of space, and a really cool place for kids. I almost want to have some kids just so I can take them there :-)
Don't forget there is also their South location that is amazing. Out past Chatfield Resrvoir. They do the pumpkin patch and corn maze during the fall and then the trail of lights in the winter. Lost of great spots.
The Denver botanical gardens really are awesome. Haven't been there in a few years now, but definitely looking forward to going back when my daughter is old enough to appreciate it more!