G R.
Yelp
I find myself down here every trip into the city, if it's nice out lunch outside, some time to check out the boats and then a walk north along the river to the Highline then back to the river all the way up to the UWS. Each neighborhood as you go through has it's own character. Although many people start here and walk north, don't miss out continuing south around the tip of Manhattan, the view will take your breath away, and some time spent in Battery Gardens will restore your spirit. From there stroll through the historic streets, take in one of the specialty museums, walk the Brooklyn Bridge or ride the ferry to Staten Island, it's free too!
I know this review covers much more than the marina, however for me it's the starting point to a great day. I've been out here when the weather is at it's best and when it's brutally cold and icy, it's always perfect to me.
I know many people consider Manhattan, too busy, noisy, dirty, etc., my answer to that is they're only seeing the negative, and they need to expand their horizons and head to the water and the parks, your perspective will change.