Bunkers are pretty fucking cool since they're very dense and can block lots of radiation. the issue with any permanent defensive structure is that while no construction is flexible in the military sense, bunkers tend to be especially immalleable. Any enemy that can see your fortifications can, atleast in terms of the surface structures, begin to meticulously plan their attack in order to best defeat the sytem. on the other hand an earthwork system can change and evolve between scouting and assaulting, and during protracted conflict can be bolstered during the fight (usually in rearward areas). another disadvantage is that generally any area in your opponents control can be captured at any time, so long as you are willing to suffer the cost of taking it. many people through history have thought their fortifications to be impassable walls, when infact history often proves them to be wagers made in resources and bet against the opponents resources, manpower, wits, and willingness.
To sum up: Bunkers can range between the most useful of military installations which protect military and civilian lives from great peril, all the way down to lowly two man death cups which may at best make two lives cost three or at worst be a pointless unplanned wast of precious resources.