Serum has one of the best interfaces I have used in a soft synth. It is very easy to navigate and inspiring in that it encourages experimentation with sound and patch creation esp once you get into making custom wavetables. It is also a good synth to learn if you are new to synthesis due to the inteligent GUI. I had the opportunity to use it for a while and I created some patches for it which are mostly pads with some custom imported wavetables.
As for sound, Serum is very clean and 'digital' sounding but a little sterile and clinical to my ears. This might fit modern and hard electronic styles but is not the ideal choice for softer warmer and more organic electronica or the type that looks to vintage sounds for its basis like classic berlin school or large cinematic sounds. What it does do well though is create patches that cut through the mix. If you mostly have analog hardware synths or software vintage emulations then serum can be a nice addition for that clean digitial sound to add an extra dimension. Its effects engine can also be used seperately so this is a bonus in that you can chain it with another synth. Its effects section is versitile and again super easy to use. If you want that pure vintage electronica sound or warm lush pads for cinematic music then look elsewhere but as a modern clean digitial sounding synth engine it is very good but not to my tastes. Soft synths like Factory make deeper and richer more organic sounds almost as good as some real hardware which often gets overlooked.
*** RECOMMENDED FOR MODERN DIGITAL SOUNDING ELECTRONICA ***