Fiona Shaw is a great actress--and she was good. I didn't think a single other actor in it was--or they were just poorly directed. Screaming all your lines does not equal great acting--which is why Fiona was especially good in contrast with all of her layers and details.
Yes, in any other show (or with better set up) that ending would have been BRILLIANT. It was truly disturbing--but in relation to everything else, it came off as contrived. After I saw the production, I read up on it--to see if my opinion would change. I was even more sure of my feelings when Deborah Warner and Fiona Shaw discussed that Medea was not crazy--she killed her children to protect them from a worse death. I agree with that. I like that they didn't see her as crazy or that the killings were an act of revenge against Jason. However, chasing her kids in their underwear and slashing their throats to sounds of hell hardly matches their supposed intention.
But--I know that there are those who loved it. And, I actually respect theatre and films that have such volatile love/hate reactions! =) Thus, I can respect this production for that--but only for that.