I have played Pinball Circus (Las Vegas version)- believe me, it's a good thing it never went into production.

The rarest Solid State game has got to be Zingy Bingy, which is probably sitting 95% complete in Python Angelo's basement. The 1995 Capcom production team were a bunch of geniuses who were having all their good ideas about a decade late. Just think how successful the company could've been if they'd launch those ideas in the late 1980s or early 1990s ! That Big Bang Bar and Kingpin were still "re-made" years later stands as a testament to their excellent design.