Depends what civ you are playing - some like Babylon, Egypt, Ethiopia and Mali are just about impossible on Emperor no matter what you do, as you can't tech fast enough to get the necessary techs in time. Others like Maya need you to do everything right from the start if you're to win. But most of them are doable if you're fast and aggressive enough, although you need a decent starting situation with ones like Byzantium and Prussia.
Which ones are you having trouble with?
All civs that have to research techs: Rome, China... They would be possible without tech UHV but because of all penalties your research speed is abysial slow and AI has so many benefits you cant succeed. Not mention Rome and China UHV requires many cities making even monarchy level challenge extreamly difficult.