Hi,
i have an ES60 and it's a very good guitar and a beautiful instrument. I wrote a review on www.harmony-central.com about it. As far as I know, is the ES120 the japanese-made model. The ES60 has very few minor flaws, but you have to look very hard. The painting on the inner side of the f-holes is not very accurate. And the binding on one horn is on one point kind of rough. But you can't see it. That's it. Maybe they spent more attantion to detail and use more expensive woods for the japanese-models.
I have a gibson firebird also, which sounds great, but had more flaws then the ES60 when I bought it (Rough fingerboard, one spring for one pickup was missing). A friend of mine has a 69 ES335. It's a great instrument, of course, but I can't see a significant difference in quality and sound. If you want to hear the ES60 click on www.chillout-bluesband.de. Under "Sounds" you will find a couple of demo-tracks, where I played the ES60. The slide-guitar is the firebird.
Greetings
Juergen