In his longer works, Ballard's ideas often wore a bit thin. In particular, his late novels (Cocaine Nights, etc.) are the longest — beautifully written, sure, but they are essentially reskinned versions of his earlier High-Rise and Running Wild, where he already perfected the motif of humans in gated communities reverting to base, animal, violent behaviour. We didn't really need those; he'd already made his point.
I do recommend getting his "The Complete Stories of J. G. Ballard" (not to be confused with "The Complete Short Stories of J. G. Ballard: Volume 1" and "Volume 2", both of which it supercedes). It includes classics such as "The Concentration City", "Studio 5, The Stars", "A Question of Re-Entry", "Billenium", and "The Garden of Time".
While I've always enjoyed Ballard's coldly satirical perspective on modern life (The Atrocity Exhibition maybe being the pinnacle of this), I think he's at his best when he gets looser and a bit weird. Nature succumbing to strange mutations feature in The Drowned World, but The Crystal World is absolutely supercharged with hallucinogenic weirdness, a fever dream that turns magical-realist in the end. Later novels touch on this man/nature dichotomy, but not as strongly as his earlier work, although late short stories like "Dream Cargoes" revisit that theme.