I just discovered this for myself this past week. I've been playing with Unity for a while now and just recently decided to give UE4 a try. I couldn't even do a serious evaluation of it on my PC with my current graphics card. I didn't have any problems with Unity at all but with UE4 I could barely open or run the sample projects. Even the blueprint editors were terribly laggy. I purchased a new graphics card and it runs beautifully now. I'm not sure how I feel about this. UE4 is definitely a lot "prettier".