Hard shells are basically designed to be the protective outer layer, and to keep water and wind out. As a result, the usual hard shell has no insulation and requires layering in colder conditions (see 3-layer principle).
While the hard shell protects you from the water pouring down on the outside, the breathability is rather limited. Some membranes work around this fact, but the risk of feeling damp and clammy inside a hard shell once you take a break from your physical activity remains. Some technical membranes are also highly priced. The better the performance and thus the waterproof/breathable-combination, the more expensive the garment will most probably be.
In any case, make sure that your hard shell is equipped with zipped ventilation areas allowing you to open part of the garment (preferably in a semi-protected area like under the armpit) to get more airflow inside and prevent moisture build up.
Hard shells are usually stiffer and heavier than soft shells. But in really extreme and wet conditions, nothing beats this kind of garment, especially when you are out there for a longer period of time like on a multiple-day backpacking trip.