The first characteristic that emerges when you start using Mellel is how fast the application reacts to actions. I attribute it to its being based on XML. The second is how styles are organised. Paragraph and character styles are separate entities, so I can have one paragraph style for quotations and different character styles for Italian, English (UK), Catalan… And there are page styles, too. In regard to both features, Mellel drifts apart from Nisus, which is based on RTF and has a more standard approach to styles.
It’s hard on everyone to start using a word processor from scratch, but many documents cannot be written in plain text. It’d be worse to pay a monthly subscription to Adobe or to buy a QuarkXPress 2015 one-time license. In my opinion, Mellel is well worth the effort.