PCSX2

So, I've tried emulating FFXII with default settings and it was ... OK.
Then I've tweeked a few things, toggled some settings and what I got was an almost HD version of the game: native laptop resolution, widescreen, excellent performance and crisp image quality. I've previously cleared FFXII on PS2 and the difference is STRIKING and DELIGHTFUL.

Difficult to configure, but the performance is great. It also has a wide community of users, so it's easy to resolve any issues you encounter. Obviously requires a powerful PC to emulate most games.

Great emu that has made some awesome progress over the years.

A lot of games are very playable.

Technically, there are other PS2 emulators, but this is the only one worth noting (of the three that I know, at least two (PS2Emu and Emution) never got out of alpha and have no homepage whatsoever, while the third, Neutrino SX2, has been dead for about 8 years, and also has no homepage anymore).

This is the one emu that slowly showed us that PlayStation emulation was truly possible... It does also have very high system requirements, though.