I thought that the 3D interface of Monkey Island was brilliant, although it did lack the atmosphere of the first two games (Not really atmospheric in CMI either).
But anyway, Let's face it. If Lucas Arts didn't step up to 3D, then the section devoted to Adventure Games would slowly gather dust, until BLAM. Star Wars games ruled the world.
The 3D-ness of Monkey Island also worked great on the PS2, and helped to create a whole new Adventure fanbase (although they might not know it yet), and the success of the game means that LEC will be willing to invest in more adventure games, such as Full Throttle 2, Sam & Max 2, Maniac Mansion 3, and those 5 new original titles that they're making (PLZ GOD).
Grim Fandango did come into its own, and worked a lot better than EMI due to sheer brilliance. You could smell the cigarette smoke. But EMI did have its moments, and deserves a little respect.
Viva la 3D gamés