First and most important you have to take this movie for what it is not your typical hero movie. I have not read any green hornet or seen any of it's shows. That being said from what I have heard and read about this movie it departs from the original representation of this character.
The GoodThis movie is funny! Seth Rogen as the lead and Cameron Diaz as a supporting actress provide plenty of laugh out loud moments. One doesn't have to worry about all the funny moments being spoiled for promotion they saved some gems for the movie. And no matter how many times I see Seth shoot himself in the face with the gas gun it never loses it's humor. The action is great. I liked the effect they used for the fight scenes of slowing down time and highlighting points of interest to explain the fighting gifts of Kato. The cars and gadgets were all phenomenal. It was also great to see homage payed to Bruce Lee in the film and I missed it but I believe a nod to the Lone Ranger might be in there also.
The BadThis thing is unrealistic. The whole concept to me is much like Batman. You have a rich individual who is able to finance and develop tools necessary to combat crime. This was kept in tact and perfectly plausible. The problem arose when the situations they escape from and the way in which they do so became ludicrous. Taking the elevator up 10 stories in half of a vehicle and then driving half of a vehicle around a office makes for cool special effects but poor believability. That said it is understood that in this genre believability is a relative term. The greater problem was the underdeveloped and rushed plot.
I will watch this movie again. I think it is a good addition to the hero movie genre. It is a look at what goofy good hearted guys attempt at being heroes would look like. If you are a Green Hornet fan though this has the potential to upset you.