Yes, PGM has some great games. I have a board and a few carts, and they have very rich colours and animations. Altough I'm not sure if they work anymore. The board has been on storage for years.
IIRC the PGM boards has more colors than neogeo/cps, 5 or 6 bits per pixel instead of 4.
The main problem with them is that latest games, like DF or the gladiator run mostly on an ARM cpu in the cartridge, used as protection.
And yes, CPS1 is an easy system. I've seen some chinese multi boards with the games already flashed. But to make a proper CPS1 board, it should support QSound games with qsound audio quality and not just using bootleg audio roms, and also have an integrated C board so it doesn't require a working one. Also making a C board replacement would be nice.
Also system16 & system18 are easy systems to make flash boards for.
Anyone with a little experience in FPGAs and board design could easily build a CPS1 (non qsound and external C board), sys16 and sys18.