There isn't a lot of argument: "Madame Bovary" is considered one of the great novels of all time. It's well worth your time. And since you're looking for an English translation, the important issue isn't "should I read Flaubert?" The issue is: "What translation?"
The first thing you need to know is that you should avoid the Eleanor Marx Aveling translation published by Dover and others (it's out-of-copyright, so it's popular with budget publishers). The Aveling translation is incredibly clumsy--so bad that I actually looked up the translator's biography to make sure she was a native English-speaker.
The translator of a newer edition, Francis Steegmuller, is an authority on Flaubert and an exceptionally sympathetic translator. While no translation will truly do justice to Flaubert's treatment of Norman dialects and his mastery of the French tongue, Mr. Steegmuller's work is sensational and preserves much of Flaubert's vibrant prose (I read excerpts in college, but am unwilling to take six months reading the original in my indifferent French). His translation is also highly readable, making this edition an easy choice--and worth the extra money over the other translations.