Maille whole grain mustards are very good, but the basic Dijon is not near as good as Grey Poupon. Something about the taste is richer and more 'mustardy' to me.
That being said, the Maille they sell in the US is made in Canada, if we're comparing the ones in France it's a whole different story...

If you want good spicy mustard, just make your own with mustard powder or seeds, adding vinegars (you can change up the types for different flavours), salt, honey, all kinds of other things. This will also allow you to control the heat to what you like. Lots of good recipes out there, give it a try.