I ended up reading a ton of Silverberg's stuff because he wrote so much. Picking where to begin really depends on what you're into. If you want a classic, high-concept sci-fi novel, 'Dying Inside' is incredible. It's this gut-punch story about a telepath losing his powers and grappling with mortality; it feels literary and raw, not your typical space adventure. That one won awards and gets mentioned in every serious discussion about his work.
But honestly, I found it a bit heavy for a first go. My own entry point was 'The Book of Skulls'. It's more of a psychological thriller with a speculative edge—four college students on a quest for immortality, with a dark twist. The character dynamics are sharp and it's got a faster pace. After that, I tackled his famous 'Majipoor' series, starting with 'Lord Valentine's Castle'. That one's a whole different vibe, a sprawling, almost fantasy-esque journey on a giant planet. It's less bleak, more adventure-driven. So I'd say if you lean philosophical, start inside; if you want a page-turner with teeth, 'Skulls'; for pure, imaginative escapism, head to Majipoor.