Sorry my ignorance but im using a full upgrated Reason 3.0 propellerhead with orchestra refills (their like Soundbanks, instruments library) and it sounds real instruments that is a fact but im curious about GPO, it includes Piano Roll? you know, like Reason or FLStudio 6. and it GPO worth the money??
I'm not sure if I understood your question correctly, but let's hope so. You can't compare Reason and GPO directly. GPO is a sound library. GPO isn't a sequencer program, where you can make music inside the program, like reason is. GPO doesn't include piano roll or any other things to make a song withing it.
Instead, GPO is like a ReFill. In fact, there will be a GPO ReFill for Reason, so you can buy GPO as an extension sound library to your Reason. This will provide you with much better orchestral instruments as included in Reason by default and you can load GPO's orchestral instruments just like you load them from the Reason library at the moment and add them to your song.
You can listen to demos made with GPO at www.garritan.com. These demos are made using GPO as a VST/AU-instrument but GPO Refill will probably provide very much the same functionality and sounds as the VST/AU-version.
Someone, please correct me if Refill is out already, but I'm assuming it's still in production..?
GPO could be used with only a computer and keyboard, where you would play GPO instruments live.
GPO is normally used with a sequencer by most of us. You mentioned a couple of the better known, and more expensive, ones. There are reasonable, lower cost alternatives if you're interested. At one point Traktion was free (Traktion 1), check that out, or follow the trail to other candidates.