Preemption is one of those issues -- along with issue and claim preclusion, exhaustion of remedies, and justiciability -- that only a lawyer can love. It's technical, messy, and a one-way ticket to Palookaville for plaintiffs unlucky enough to bump up against it in their state-law-based tort suits.
Preemption starts off easy: Under the Supremacy Clause, federal laws take precedence over state