Strangely, it doesn't feel too bad with normal vision. Yes, the barbs are far more terrifying, but it gives extra incentive to explore and guard precious Settlers using cheaper units. No more sending Settlers out by themselves and moving them 1 tile at a time to be safe. It also makes you pay more attention to diplomacy and send out even more scouts and spies to keep eyes on your neighbors. Having units that move twice as far as normal lets you quickly move from hilltop to forest if you think barbs are nearby too. It's definitely a different flavor of civ. Buildings matter, scouting matters, unit promotions matter, everything slows down with the expensive techs. It certainly feels better than regular civ in many ways, but I'd have to play GEM on Normal Speed to give any kind of good opinion. One (downside?/upside?) is the windows to exploit tech advantages against the AI are much larger in GEM. Like drafting rifles might allow you to kill 1AI is BTS Deity Normal Speed, but on GEM with faster units and double tech prices you could conquer 4 or 5 civs before the AI caught up and closed the window.