I had the Focus S from launch day until Monday, when I returned it for the Titan deal at Best Buy. The only things I've noticed are the inferior black levels and lower saturation, but these aren't much of an issue at all for me. The screen size is impressive. Not for everyone I'm sure, but I love it.
Also, aside from the screen, I like some other aspects of the Titan over the Focus S (and every Windows Phone, basically), such as the indicator light, the metal body, the vibration, HTCs attentive phone settings, the panorama camera mode, and the capacitive buttons that are always on when the screen is on. It always bothered me that the buttons light up only after you touch them on the Samsung phones. What's the point in them lighting up after you've already hit them?