What was the merit of the Sega Genesis system (circa 91)?

Answer 1

The biggest advantage the Genesis had was that it beat the Super Famicom/SNES to the market (by two years in Japan). It also had great "edgy" advertising that appealed to older (teen & up) gamers.

Technically, it used the Motorola 68000 CPU, a 16-bit processor running at about 7MHz. The SNES, on the other hand, used a version of the WDC65816 which is a 16-bit version of the famous 8-bit 6502 processor, and it was only run at about 3MHz in the SNES. But what made the SNES shine was its PPU (Picture Processor Unit), which beat the graphics in the Genesis in resolution and colors. The chip in the SNES also had "mode 7" for pseudo 3-d graphics with hardware-assisted rotation and scaling.

But you were asking about the Genesis, weren't you? It's advantages were CPU speed, the advantage of being first to market, appeal to older gamers, and edgier titles...specifically, Sonic the Hedgehog, which was louder and faster than any of the Mario games.