After using UE4 for a while I have to say it is leaps and bounds better than UE3 but there are a few simple features that I would love to see return or be added to UE4.
Geometry Editor:
In UE3 the geometry editor showed a very nice clear visual representation of where it intersected other meshes or geometry making it much easier to do things such as blocking volume passes on levels or simply seeing how your brush intersects with other objects accurately. I know this currently happens on the edge of a brush but it would be nice if this was extended into the face/surface of a brush like it was on UE3.
Movement feature:
In UE3 there was a very handy feature at the bottom of the screen that I used all of the time that showed you how far you have moved something from its current position. This was very useful for measuring things out or for doing specific sizes of areas, such as duplicating a mesh and keeping it 1024 or more units apart from the opposite mesh for gameplay reasons. I know I can measure things after moving them but it was a very handy feature to be able to see the distance an object had been moved in real time.
Widget orientation:
This one is pretty minor and there might be a reason this doesn’t already do this such as wanting to keep the arrows pointing in the positive direction but when you want to move a mesh using the widget it would be nice if the arrows on the widget oriented in a direction that allowed you to click them properly, currently you can not click the central part of the widget very easily unless you get on the other side of the widget and click it. Hopefully this pic helps explain a little better 
Thanks!