-The fact that geoserver is open source and is based on OGC and has a clear laid out user documentation provided on their site. Being open source is a bonus when compared to ESRI solutions which can cost substantially more, this is a huge plus for a SME especially given current circumstances.
-The source code for geosever is very accessible
-Works very well with postGIS and handle Raster data with ease, I've found geosever capable of handling even our most storage hungry datasets Review collected by and hosted on G2.com.
-Installation / tweaking an install was perhaps not the easiest but nothing to fear. S
-Can have issues when reprojecting into some co-ordinate reference systems.
-Personally struggled to get geosever accessible over https
-An obvious downside of geosever being free is the lack of support you would receive from the paid solutions ESRI provides. However there is a wealth of information, tutorials and help to be found for geosever. Review collected by and hosted on G2.com.