This is a classic kdrama that I think everyone should watch.
However, being a classic, and despite me giving it a high rating I wouldn't consider it a great drama. It's very cliche: rich boy, poor girl. There's the typical love triangle, there's a bad boy who only has a soft spot for the female lead. There is also the "evil" family that wants to keep the main leads apart. It's all very predictable.
However, the acting is what makes this such a great drama. Every character is great and portrayed so well. The casting was perfect in my opinion.