Vibhor, do visit places like cochin & allepey. do enjoy the backwaters in allepey. you will find metro cities anywhere else but you wont find the calm & serene atmosphere of allepey & the houseboats elsewhere. by the way, allepey is my native too! its a big time favourite destination for tourists.
do go to munnar & tekkady. IMO, these are the USPs & special attractions of kerela. if you just come to kerela & roam around in the capital city, its of no use.
points to remember:
1) in a hotel, order only traditional kerelite food. order for fish curries & "kerela parota", they are a yummy combi.
2) its raining heavily there, so be prepared.
3) enjoy the scenic beauty & stay in traditional cottages rather than 3 star/5 star hotels!
if you plan to visit allepey, come down by 11am, see the place & then hire a houseboat for a day & night. you will usually enter the houseboat by 2-3pm, you can spend the night in the boat (it has bedrooms, AC, everything for your comfort) & next day moring 11am, you will be offloaded!
enjoy God's Own Country!