It can be absolutely dreadful. I had an infestation of them.
As mentioned beer traps are effective, slugs follow their trail home so leave beer traps near the trail. If you catch lots it's fairly disgusting but get rid asap as the stench is horrific. Salt directly on them kills them, as does spray bleach. I had some success with nematodes but l think the timing of using them is fairly crucial for effectiveness. Eggshells, copper wire, many other suggestions do not help if the number of slugs is high, they get hardier the longer they live and multiply at a rate of knots.
Finally, and fortunately, I moved (not because of the slugs and the midnight death forays, but because l found a house with a view (and very, very few slugs).