Are cliff hangers a good thing or bad thing?

Last year I started a novel, when I came up with an ideal for a second book to it. So I stopped working on it to work on the plot for the second book. I figured if I did all the ground work for both books first. I could do the actual writing all together for both. So for the last month or two I've been working on the plot for the second part. But I have this ideal to do a cliff hanger that would bring it into a third book. I'm not sure I should write a third part to the story because I know sometimes sequels can ruin something that was already good. But I have this gut feeling to go ahead with and try. But the problem is coming with ideals that could extend it. Because with the second book I feel the plot is basically done.