It’s not that hard to find info about advantages of UE4, but it’s hard to find info about disadvantages and hidden problems with the engine. Can you share some?
Performance, can be rather unstable at times although it’s a lot better now than it was. The iteration speed is a lot slower than Unity IMO, but I suppose it depends on what you’re used to as it feels to me you have to understand Epic’s way of doing things. Which isn’t necessarily a bad thing as who’s to say Epic’s way isn’t the right way?
The UI for the editor has gotten mighty fat and a little convoluted, I’d also seriously consider the size of your game if you want to release it to the public (again performance).
Apart from that, it’s probably the most impressive engine I’ve ever seen.
One of the main disadvantages is, that for some people the engine isn’t so stable, but as epic games always updates the engine, this isn’t a big problem 
-> when you get any crashes or bugs, make sure to report them on answerhub: https://answers.unrealengine/
I think the biggest disadvantage for me is the binary assets the blueprints are written out as … this plays hell with out source code server … Epic has mentioned they are looking in to something … but I can’t find the link now.
The editor has crashed on me a few times (never Ctrl-C and Ctrl-V in the Widget HUD editor) … but these bugs have been reported and they are working on it.
Networking (or Replication) took a bit of getting used to … but once I got the hange of it, it has become second nature to me when I am making a game.
Not everyone will find UE4 to their tastes, ultimately it is up to you to decide. However now that UE4 is FREE, it is easy for you to get the engine and try it for yourself to make the decision. 8-}
I personally am very happy with UE4 and will continue to use it for my projects.
for me, its the performance (mainly), the constant crashes, the many many bugs, the constant base code overhauls, huge package sizes, lack of basic features and lack of (or unhelpful) documentation.
One of the disadvantages from me is the lack of tutorials from the community, Unity has a fairly good range of tutorials from the public but I’m guessing thats due to more people using it over the years as its been free. Since UE4 is free more people will be using it and I’d say there is going to be more tutorials from people using it
I’ve seen quite a few user tutorials on YouTube, and we have a section here devoted to that which seems to be fairly active. I think one of the biggest obstacles is time. At least in my personal experience it is, I would like to do tutorials but I’ve been busy with the marketplace content. It’s definitely on the docket though.
Not being able to build cross platform (i.e. us a Mac to build a windows exe etc.) and probably more importantly (as of yet) none of the new cloud services Unity are rapidly building, build/ads/analytics/data etc.
blueprint makes it hard to keep the visual coding clean and organized during prototyping.
nor u can edit blueprint during gameplay.u had to restart the game from beginning for each simple modification.
blueprint could be a a dreamy part for non-coder.
but for programmer it is hard to adjust with it.
a textual scripting language could have solve all of this.but epic not going to do that .
ue4 is far far away to be ready for mobile games.
specially for android.
package size is most probably worst of all engines i have used.
+it does not have a android remote testing option.
epic have no plan to give that option in near feature.
so ue4 would be a vary bad choice for android developer.
For me, it’s bad performance on mobile and low-end pc and huge runtime memory usage. But as heavy as UE4 is, it’s still joyful engine to play with.
Maybe I’m missing something obvious, but it doesn’t seem like you can edit variables in UE4 while you are playing the game. This is super easy to do (and very productive) in Unity.
Besides some crashes, which are sometimes bad, sometimes not (But can always quickly recover from), the lack of a more sophisticated landscape modelling editor is bothering me too. Just look at Project Spark level editor, than you know what means to model a world in no time. Additionally, i think it is to complicated how to deal with getting basic lighting right - just starting with that topic.
The worst in Unreal so far for me, the way landscape holes are implemented… seriously, super complicated. Just let me dig the landscape, with one simple shovel tool.
As of UE 4.7.2 I’ve been getting random crashes - even with autosave disabled and I’m away from the computer, I come back to find it has crashed - 4.7.4 is still doing it - have never heard back from Epic when submitting the bug reports - is anyone else experiencing these sorts of crashes?
I have had my share of stability issues and also realizing there’s a lot for me to learn with lighting.
I wish there were more character models for the Unreal 4 skeleton on the asset store since modeling/rigging/3d animation is one of my biggest weaknesses.
It’s still amazing to me that Unreal 4 and a ton art/programming assets are free compared to what it takes to have similar results in Unity 4 (in my experience)