The timing was simply wrong, but Sega's 32X add-on for the Genesis is a lovely way of upgrading your 16-bit Sega console, what with its two RISC processors, the powerful graphics chip, the improved sound and the extra memory. Sadly, the console flopped and only 40 games supporting it were released.
To play with one, you could do much worse than bidding on this boxed Sega 32X. It the US Genesis version, it comes complete in its box and is accompanied by the rather brilliant Star Wars Arcade (boxed, complete) cartridge. Seller ships mostly worldwide.