Similar atmosphere and general plot devices. A male lead that is nearly alone in this world who gets sucked into a mysterious, dark plot connected to their past. Tons of action, investigation, plotting, revelations, kidnappings, etc. While City Hunter's characters and plot are a bit more sophisticated than Two Weeks, both are still enjoyable.
Quite a leap from melo to action thriller - but City Hunter is also a revenge thriller and it's great to see how very different a basic premise like that can be handled. It also handles themes such as is love weakness? Do you need to hide yourself emotionally to be successful or to survie? Plus another lead pair with superb chemistry; really welll acted evil mastermind, a truly comic retainer in the City Hunter's ahjussi; and a cute bromance!