I actually watched this drama because I saw a viewership list, and saw that close to 40% of Seoul was tuning in to watch Boys Over Flowers.  Truthfully, I watched it because of it's widespread popularity.  Here are the pros and cons.  
Note:  Contains spoilers!
  Cons:
1.  Goo Jyun Pyo is a jerk.  Why the protagonist fell for him is beyond me.  
2.  You might learn some "mean" vocabulary or wrong phrases, as one of the characters says a lot of phrases incorrectly and is quite mean.  However, he is always corrected on screen.  
3.  The characters make a lot of really idiotic decisions.  However, this is what makes it a drama -- right?  
 
4.  Stereotypical drama plot:  poor good girl falls for a mean rich guy.
Pro:
1.  You get to see what they eat for breakfast!
2.  There's a scene where they make kimchi.
3.  You'll understand the sitcom jokes about the show.  
4.  Good looking guys and girls -- though this is almost a given with a k-drama.    
 
5.  The little brother is really funny.
6.  You get to see the inside of a porridge shop.
I hope that helps!