In my opinion, firstly it is the characterization of Shashank that really helps this pairing....he is Ekta's most unique male lead in many years now....the last time I thought Ekta managed to create a very unique and multi-layered male lead character was that of Prem in KZK.....Shashank is deffo not Prem but he is unpredictable in his own way and that is what I enjoy about him.....I like his impulsiveness, his goofiness, his tendency to say what's on his mind in a straighforward manner, his childishness, his endearing confusion, his emotional side, his 'take charge' side, his stubborn side....there are so many aspects to him...that's what makes things interesting....and what really helps all this is the fact that Vivan is playing him so well too.
Also if we come to the pairing...like ppl mentioned before...the fact that BOTH these actors can act...unlike most pairings on TV today where usually one actor is the saving grace of a pair.....VK have natural, understated chemistry and they compliment each other very well in terms of the way their characters play off each other...whether is the lighter, comic moments or the deep, intense moments...they pull off everything with this classy sort of elan that makes for good viewing.
And the scenes given to them albeit appearing cliched on the surface, are actually well written and well directed....great dialogues which make the moments b/w them more touching and endearing....all this really helps.
Now knowing Ekta's track record, they are bound to go down the drain eventually....lol....but I'm liking them as of now.....cuz they are the freshest pair Kekta has produced in a while :-)