G Major and E Minor contain exactly the same notes (G, A, B, C, D, E, F#), but the difference is in the way that the PLAYER emphasizes these notes. You say that when you played in E Minor it sounded good, but it sounded bad in G Major. Well, the reason is the way that you approach and play the minor scale as compared to the major scale. Both should work fine. The safest scale you could use would be the G Major Pentatonic (or E Minor Pentatonic scale where once again, these have exactly the same notes). This way you avoid heavy tension notes like the 4th (C) adn the 7th (F#). Try it out and tell me how it goes (although I know it should go well, because I've soloed over that progression many a time with old G Major Pent...)
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster
