We loved, loved, LOVED it! In fact, it was probably the most "Disney" moment we had on our entire trip. There is something absolutely magical about being on the 15th floor of the Contemporary Resort, having an awesome meal, and then watching the fireworks from the balcony. The only complaint we had was that the people around us would not stop talking and we could not hear the dialogue. That being said, it was absolutely incredible.
Oh, here's a tip as well! As you probably know, when "Wishes" gets over with at MK, there is a rush to get to the exit and the buses. If you are staying on property, here is a good strategy: after the fireworks, we got on the monorail, got off at the TTS and switched to the Epcot monorail. The buses were still going at Epcot and we just walked right on!
We will be making our 2nd trip to WDW this coming May, and California Grill will be one of the first reservations I make.