In 1994 my country switched from first past the post to MMP.

Incredible fear mongering was put about (and sometimes still is). But despite our near brushes with craziness (like Kim Dotcom almost buying his way into parliament) the situation now is immeasurably better than when we had political parties who did not have to compromise and cooperate. Everyone's more...reasonable.

To an outsider it looks like getting rid of the two party system would be a great thing for the US.

MMP can actually over-represent minority interests by putting minor parties in power-broking positions. But I agree it's an overall improvement.