You should have been there — the concert was incredible.

'should have + 过去分词' 是情态动词 should 的完成式结构。此处用于叙事修辞：说话人以 'you should have been there' 唤起听者对当时到场体验的想象，强调现场的精彩程度，而非表达后悔或批评。