I've pretty much beaten the topic of comparing the ES to the Phantom to death. Just search the forum and you'll know what I mean. Actually to think of it when the ES series were still Yamaha's flagship synthline there were a ton of threads on comparing it to the Phantom triton etc.

In short what I like about the ES is that you can expand it with different synth engines (rather than just more samples on expansion cards). The most important factor for me however is that all sounds on the MOtif work well in the mix. On Roland and Korg synths they kind of sound great in the patch mode but really don't work that well in a multitimbral context. Actually Korg are a bit better in that respect. ALthough still not as good as Yamaha.

That 'bout sums it up. Oh, and I also like the keyboard feel of the ES8. Out of all the weighted action keyboards (excluding the later MO and Motif XS synths of course) it is simply the best. If you like weighted keys that is.