I like Gluck a lot, and this Iphigénie is my #2 after Orfeo & Euridice (the other Iphigénie is good, too - most of its arias are quite short but it has a very nice overture). This one is, or ought to be, very dramatic.
I saw Susan Graham in the title-role at Covent Garden a couple of years ago, with Paul Groves excellent as Pylade and Simon Keenlyside chewing the scenery as Oreste. Good production, with quite a lot of dancers. I listened to Act 1 on the radio last night, and thought that Domingo sounded rather frayed.