We love Boma--really love it--we went 3x during our recent 2 week stay.
We also tried Tusker House for the first time, and it's now on our must do list. The food is similar to Boma, but different, if that makes sense.
If you can't get to Boma, Tusker House would be a great alternative. It's much easier to get to (I got really sick of all the bus rides to and from the AKL) and has more convenient hours (I so wish Boma served lunch).
Enjoy!