Can you list some "oppa" romances that you think I should check out? Thanks ^^

What do you mean with "oppa" romances? Bromance romances or romance between younger woman and older man? ^.^
more so younger girl/ older boy :) shows where the word 'oppa' is used by the girl protagonist :) 
Reply 1997 , Reply 1994 , Mary Stayed Out All Night , Prime minister and I , Marry him if you dare , Liar game , You're all surrander ,Pretty boy ,Arang and the Magistrate , I miss you ,Take care of the young lady , ,Hope for love , The moon embrace the sun , she is so lovable , My girl , Deligthful girl ,Lee Soon Shin is the best ,Operation Proposal ,18 VS  29 , One sunny day ,Her lovely heels ,Warm and cozy ,I order you , Blade man ,Angel eyes ,When a man loves ,Doctor stranger ,rich man poor woman ,Cyrano agency ,A gentleman's dignity , Noble my love ,Two weeks , oh ! my ghost ,Three days ,The Princess' man ,Tree with deep roots , Dream high , Dream High 2 .
My Love Eun Dong! It's such an underrated drama with oppa romance! It's really romantic! It's the best drama I've seen so far. When the girl says Oppa :D OMG so good haha!