Kog'Maw is not very good for assaulting Windmill, but amazing at holding the bottom point. He can easily push the enemy solo out of the lane, and with his ultimate, can keep anyone from even attempting to cap the bottom control point.
Furthermore, since much of the game seems to be overloaded with tanky DPS that stack HP, and glass cannons, Kog'Maw can remove many of them from the fight without putting himself at risk. The key is wise placement of E. If anyone does manage to get in your face, however, you're toast. Abusing your range is paramount to doing well, and since he scales so well with items, you'll find his damage output sufficient to duke it out with some of the toughest in Dominion.