Piano: I think they are pretty good. You'll see mixed reviews on these. Some people say they're phenomenal, others say they're terrible. I think they work well in a mix. Not sure about by themselves.0
Organs: Not a big fan. I haven't had it for too long so haven't dug too deep and had a chance to tweak much but so far they sounded thin to me. I'm partial to the organ on my ASR-10 anyway so don't normally use them much.
Strings: Excellent. I love the strings. Roland always does well with the strings in my opinion.
EPs: Excellent. This is one of my favorite areas. There are many different patches and I think they all sound great.
Check out the information at the Roland Clan forums. There are several reviews over there. Also, there are several pretty good reviews online if you search for them. SqueakD is on Roland Clan and also has quite a few videos on youtube with patch examples. You may want to check them out as well. Also, I think he has used both keyboards as well so you may want to try to hit him up on Roland Clan to see if he can give you more info.