The Ultraboost's reputation is built on comfort, primarily delivered by the exceptional BOOST midsole. It provides a uniquely plush yet responsive feel underfoot, effectively absorbing impact from concrete and cobblestones. During my own testing on a high-mileage trip to NYC (averaging 25k steps daily), the cushioning was genuinely impressive – my feet felt significantly less fatigued compared to previous trips using other sneakers. The energy return is noticeable, providing a subtle 'bounce' that helps maintain momentum. However, the Primeknit upper, while soft and adaptive, creates a very snug, sock-like fit. While this feels secure initially, I found that after 5-6 hours of continuous wear, the snugness became constrictive, leading to pressure points. Many users echo this, recommending sizing up half a size and noting they might not be ideal for \*all-day\* wear if you prefer a looser fit or experience significant foot swelling.