Do you have any specific examples? In 2.4 (years ago) it was kind of weird but it’s way better now. The only things I can think of is that right click select is the default option (you can change it to left click select in settings) and the default keymap isn’t really optimized, but it’s not too hard to set up your own keys.
I think Blender is pretty known for animated shorts like https://www.youtube.com/watch?v=mN0zPOpADL4 and the animation tools are strong in general (with constraints, in-betweening tools, pose library and more). I haven’t worked with mocap though, only keyed animation but it works great for that. Especially when using the addon/branch that gives smoother interpolation between keyframes:
real smooth auto beziers for animators - Latest News - Blender Artists Community (addon version)
New F-Curve Smoothing mode in review for 2.8 (with 2.79 RC test build) - Blender and CG Discussions - Blender Artists Community (branch version)
There’s a picture here real smooth auto beziers for animators - Latest News - Blender Artists Community that compares Blender (using the addon), Maya, Max and Modo, without manually editing the curves.
The only thing you need to keep in mind for using Blender with UE4 is that there’s an UE4 bug that requires you to use 0.01 unit scene scale to not mess up the scaling of animations.