Boys Over Flowers is certainly classified as a "must-see" in the K-Drama universe, and I think it's a great 'starter' drama for those wanting to get into the mix.
It's a 2009 drama, so this helps to give viewers an understanding of the flow of a drama and what to expect in a formula as well as familiarise yourself with one of the most common tropes (Rich guy / Poor girl), which in this setting was both enjoyable & frustrating.

I thoroughly enjoyed the dynamics of the characters interacting with the female lead and the sense that despite the clear romantic intention between Lee & Gu's respective characters - it played on the Reverse Harem concept (reference Japanese manga Ouran High School Host Club as a prime example of this).
I found this quite fun and enjoyable on screen, and really helped in some parts to drive the story.

When watching this drama, I became incredibly invested in the characters and it was a really enjoyable watch, but I couldn't attest to rewatch value.
The overarching story at times can be repetitive - which I can only attest to after having watching a few more dramas, but the way this is done, if you start with this drama, it will flow nicely and be less obvious in it's repetition.

The story follows a high-school setting, and flows well in regards to the character struggles, obstacles they have to overcome and when it reaches the conclusion it ties up really nicely.

These is probably one of the easiest dramas I've watched, and wasn't high angst and involved a lot of entertaining and sincere friendships on screen.
I certainly recommend this as a beginning drama and I am glad this is the one I started with to get me into the K-Drama world :)