Warren Buffett has loomed large at Berkshire Hathaway's annual shareholder meetings, and this will be a key challenge as new CEO Greg Abel takes center stage.

For the first time, the 95-year-old Buffett won't be the central figure on stage, marking a new era for one of investing's most closely watched rituals.

The mood in the air was cautiously optimistic as new and returning investors weighed the company's direction under a new chief executive.