You can spend a truckload of money on sets and costumes. You can thrill viewers with showy lighting effects. But at its core, memorable theater is about performance. This season the Repertory Theatre of St. Louis delivered vital performances in spades. There was Lori Wilner's hardened mother in Brighton Beach Memoirs, the beautifully calibrated work of Mark Anderson Phillips in Clybourne Park, the scorching performance by Denise Cormier as the desperate protagonist in David Lindsay-Abaire's Good People and the haunting poignancy of Rita Gardner's headstrong grandmother in 4000 Miles. Don't forget that the entire ensemble (led by the deft John Scherer) turned The Foreigner into a breezy comic romp. The Rep is the place to see actors young and old strutting their stuff. In addition to staging nine major productions at the Loretto-Hilton and touring the Imaginary Theatre Company to area schools, the Rep presented its second season of new play readings and was the official presenter of War Horse at the Fox Theatre. Not content to rest on seniority, the Rep seems to be more ambitious than ever — and those ambitions are resulting in consistently high-quality theater.