Its styling was ugly as sin.
Some background and technical details can be found here. I've never driven one, but I've read here and there that it was an okay vehicle if one was inside it. I was in Italy a few months ago and noticed that a number of Multiplas were still on the streets of Rome and Palermo.
The odd styling was recognized as a barrier to sales, so the Multipla was given a facelift in 2004 that eliminated its worst quirks.