Zealot is pretty challenging,it gets much worse the more you progress,there are some bottleneck areas that are more like luck based
You are constantly low on ammo,health so you are forced to improvise...game allows you that
You die at bottlenecks because you are not exactly sure what to do,in other sections because you want to conserve ammo...you have like one second to think and then you are dead,so don't think
Just don't miss
Hardcore mode is doable,you would just have to space the saves properly...like demi said
and have a lots of free time