Just one of these, for example, is that when you want to make an interactive liquid, it's surface can only be a rectangle (FluidSurfaceActor). This issue is quite popular and been discussed on the support forum. It's not a big deal when you know about it: you just find a way around or design your game considering this limitation. But for the first time it really makes you ask: "Why? It's such a small thing, it shouldn't be like that!".
And there are many other small bits like sluggish material editor with no option to create a material somewhere else, Kismet for everything (I am a programmer, I prefer to type commands not to "draw" them), Ctrl+S to subtract geometry...
If the engine hadn't been awesome in the first place, these small issues woudn't bother much. I think it is in a human nature (or in my own nature?): if something is really cool, I want it to be perfect. And it upsets when it's not like that.
I was so moved, so I made a comic!
