Mixed. A reliance on assets leave you vulnerable for when they aren't updated or are abandoned. The build process has become really bloated now. Gigabyte temp files that aren't removed. Android builds taking 10 minutes where they used to take 2. I've experience going back seven years where I used a UI asset called NGUI which is very powerful but a bit odd to use, and then you face choices like whether to stick with that devil you know or try swapping to the updates Unity stuff, seeing as it's always updating.
The tools are so-so integrated. Build and run to UWP fails for some error, and you don't have real support, only the forums, but at least Unity Tech provide someone offering support. But some bits are plain buggy. I was asked to provide a bug report for the XBox One keyboard issue and it kept crashing on upload at 50%. Things like that are very frustrating time killers, where progress gets stone-walled just trying to get the rudiments of build and debug working. Today I mostly wasted trying to create a test scene to track down my UWP problem. ionAXXIA is built on 2019.2 and I don't want to try 2019.3 yet as sometimes when you upgrade a project, stuff breaks, so you stick with what works. But trying to downgrade a test project from 2019.3 to 2019.2 just crashed Unity, and I couldn't create a new 2019.2 project, with Unity defaulting to the latest installed, 2019.3. There's a good amount of wrestling with tools and libs rather than creating working code and solving game problems.
The latest Unity's are much better integrated with the tools though. All the Android stuff is downloaded and linked without having to follow a shopping-list of instructions. Swapping between platforms is pretty seamless. Press a button and bang (a slow, 2-5 minute bang), you can now build and run on Android; bang, now build and run on Xbox. The accuracy between editor and devices is also very good, allowing previews in all the different aspects. UI was created at 4:3 for iPad and then spaced out to fill wider aspects.
Looking forwards, there's a fair few unknowns. For networking, do you use the old lib you know, or try the new Unity stuff? For rendering, do you try the new LWRP or stick with the standard renderer? The R&D on solutions itself is quite costly.
But of course, if you are aiming for a multiplat release that's not constrained by engine to certain platforms, Unity is vast and capable and these issues we battle with are part and parcel of game development. The systems are soooo complex that it's always going to have struggles no matter what choices you make.