Once upon a time, the ICA blazed a trail for contemporary art in London. In 1975, the genial Belgian conceptual artist Marcel Broodthaers exhibited Décor, a landmark anti-colonial installation featuring a lobster, deckchairs and Kalashnikovs. In 1991, the ICA staged Damien Hirst’s first one-man show. There are still occasionally memorable and sizeable exhibitions — such as Jonathan Monk’s in 2005 — but over the past 10 years the institution’s impact has steadily diminished, earning it a reputation as a great café with a small gallery attached. Why?