Absolutely the pinnacle of the C4 technology, and a world-class car.... for the late '80's/early '90's. Nothing is a problem on that car, except the engine. Not that it was a problem, but parts are. I know a couple of C4 ZR1 owners, and they have to buy up whole engines/drivelines for parts, because new parts just do not exist (blocks, cylinder heads, etc).
The engines were designed by Lotus and manufactured by Yamaha. There haven't been any new parts made in over a decade, if I remember correctly.
That being said, if I could find (and afford) a red 1990 ZR1, I would park it in my garage and put a prayer mat next to it, and tell it how beautiful and awesome it is every single day.