Giant Robo is like a casserole; some bits are incredibly tasty, and some bits you have to push to the side of the plate. I love most of the incidental characters, especially the bad guys. The scenes where members of the Experts of Justice are facing off against, members of the Magnificent Ten and Big Fire (even the names are cool) are well done. When Ivan the Terrible shoots across a room and his scar glows red, all you can say is "Wow!" Also, several of the non-fight scenes are very well directed, with a lot of atmosphere. There are multiple instances in each episode where one of the good or bad characters does something that just makes you exclaim with joy at its coolness.
The problem with this film is that it dwells far too much on big stuff: Giant Robo, cities blowing up, big black orbs trashing out Shanghai, etc. Some of you will say "What do you expect from a movie called Giant Robo?" I have no answer to that. I guess this is what many people want to see. For me, long drawn out animated devastation loses its appeal after about five minutes, especially when they show the same bit of demolition multiple times (i.e. Bashtaralle getting blown up over and over again). Also, the little boy who controls Giant Robo just put me to sleep.
This would have been much better if they called it the Experts of Justice, and left out all the big stuff, including Giant Robo. But judging from the other comments, there is apparently an audience for animated cities getting trashed, so who am I to blame the filmmakers.