Introducing new adult readers to fantasy can be tough since so many of the best books are dense and challenging. I'd never ask a first-time reader to start with The <em>Lord of the Rings</em> or <em>A Song of Ice & Fire</em>, even though they're my favorites. I'd say Brandon Sanderson's <em>Mistborn </em>is a solid, well-rounded choice. It's fun, not too enormous, and the world-building isn't too advanced. My most common sales pitch for it is that I think it paces similarly to <em>Harry Potter</em>, as, even though it's more mature fantasy, there's an aspect of young(ish) characters uncovering a mystery.