Advantages:
* It looks very pretty (arguably). The window theme is aesthetically very good looking. Some might prefer Gnome's look.
* It is "fast". I found it to be faster than Ubuntu in terms of normal actions like opening apps, power off, power on etc.
* Hassle free for the most part. If you don't do anything crazy, it works smoothly and is very low maintenance.
Disadvantages:
* Tons of bugs. A lot of bugs have not been fixed since a long time. So, if you find a bug, be prepared to fix it yourself.
* eOS devs also make their own Code editor, Mail app, music app, videos app, photos app, calendar app. Some might say that this is a waste of time.
* No minimize button. And this is a little frustrating. The devs want you to use the workflow they recommend to the point that they went through the effort to hide the key and make it so that you can't enable it.
Well, for some people that is a pretty big advantage. I'm on Ubuntu 16.04 now, running Unity. Despite all its bad press I love Unity - it perfectly fits my workflow and just gets out of your way. (Not like Gnome Shell, where a third of your screen real estate is gone just with various menubars, each of which you could park a truck on.)
Gnome Shell on 18.04 pretty much killed Ubuntu for me. Next time I set up my computer, I'm going back to Elementary. (I used it some years ago, but it was still very buggy. I'm hoping they've fixed some of those since.)
Yeah, I'm still using unity 7 on 18.04. I see that it is still working in 18.10 and quite likely on 19.04. Hopefully, it'll last another LTS cycle. Technically, it should continue to work as long as xorg isn't dropped, which probably won't happen anytime soon. The only downside is that unity7 is so closely tied to ubuntu that you can't use it with any other distro. I generally like Fedora/RHEL like setups for servers, but I can't use anything other than unity (right now) for laptops.
