I adore this episode so much. It is absolutely hilarious and has many celebrities featured in the storyline (even though they are voiced by other people). I am a great fan of the Godzilla films and this episode obviously tries to spoof them as well as including spoofs of other Japanese monsters like Mothra.
I love everything about this episode apart from Kenny's death, it was poor and you could tell the writers didn't think of a cleverly plotted one. Probably because they had to think more about the main plot which anybody can understand and forgive them for. Mecha-Streisand's roar sounds a lot like the official Godzilla roar which I think is good.
Overall, I think this episode is the best episode of South Park ever and is definately worth watching.