Why was the PS1 so successful despite being a newcomer?

[Mummelmann]

It had tech that no other machine did, used CD-ROM which allowed vastly bigger games. It also got massive 3rd party support, developers had been screaming for alternatives after the mafia-like tactics and licensing hell of both Nintendo and SEGA. Nintendo's treatment of Sony during the infamous CD-ROM driven Nintendo console did nothing to help their reputation in the industry either, paired with their price fixing on software this was the final nail for 3rd party support. Another oft ignored thing the PS1 managed was to bring classical arcade games and gaming into the living room, like modern beat 'em ups and some decent rail shooters. It even got some PC-centric fare in games like Warhammer: Shadow of the Horned Rat, Warcraft II, Command & Conquer, and Diablo. The breadth of software was beyond anything Nintendo, SEGA, or the likes of Amiga or Atari had ever shown. It continued, at least in part, the traditions of Amiga, Arcades, Nintendo, SEGA and PC all in one. The PS1 also consolidated Japanese and Western games development and design in a unique way.

Proper game saving, more modern controllers, CD-ROM, massive support and immense breadth of software with some crazy hits and new IP's like Gran Turismo, Ridge Racer, Resident Evil, Tekken, Tomb Raider, and Crash Bandicoot, to name just a few. It was also probably the first console to ever reach out to a more adult demographic and not mainly kids, console gaming was still very much a guilty pleasure for adults in the mid 90's. To underline this, they released a Slim version, the first case of a proper, complete hardware revision to extend the life cycle of a home console and keep consumers interested.

In some ways, the PS1 was a hit due to other companies making big mistakes over a long period of time, but it was also a fantastic machine in its own right and did some never-before seen things in one neat package.