ePSXe was one of the major steps for the PSX emulation scene, like PSEmu Pro, bleem! and VGS were when the got released. A team of 3 developers, who worked on the project in silent for over half a year, developed the best emulator at that point, and with all the updates which followed, still up to today.
ePSXe is based on the popular PSEmu Pro plugin system, and utilizes the graphic, sound and CD functions coming with these - PAD plugins aren't supported, that's a built in thing already.