Start with what this town is not, because the alternative is a disappointing first evening. Fort Walton Beach is a family beach and a military town. There is no adults-only resort strip, no wine-bar quarter, no spa district, and the nightlife is a handful of beachfront bars on Okaloosa Island plus whatever is happening downtown. If the holiday you have in mind is a walkable evening of cocktail lists and small plates, that is Destin across the pass, and it is fifteen minutes away.
What this side gives two people instead is space and arithmetic. Because the town sits on the north shore of Santa Rosa Sound, the sun goes down across open water from the mainland, which is an accident of geography most Gulf beach towns do not have; from Fort Walton Landing or Liza Jackson Park you are looking west down a channel rather than at the back of somebody's condominium. Because the beds are cheaper here than east of the bridge, the boat is affordable. And because this is not a couples destination, the beach in February is genuinely empty.
That last point is the strongest argument on this page. From roughly January to March the Emerald Coast runs on winter long-stay visitors, daytime highs sit somewhere in the mid sixties to low seventies, the Gulf is around sixty and too cold to swim, and Okaloosa Island's twelve miles of white quartz sand have almost nobody on them. You will not be swimming. You will be walking a wide empty beach in a jumper with the water still running that improbable green, and there is a version of a romantic week in that which July cannot supply at any price.
The water is the other half of it. A private charter here costs what a shared seat costs in more fashionable places, and two people on a small boat with a captain who knows the tide can have the East Pass jetties, an empty stretch of Choctawhatchee Bay and a sunset run back through the sound without seeing another vessel outside the summer months. In late October, Crab Island — a bar that carries hundreds of boats in July — can be flat, green and completely deserted, because the licensed vendor barges only anchor between the first of March and the end of October.
So the shape of a good trip for two here is: sleep cheaply on this side, spend the money on a boat and a table, use the shoulder season, and cross east deliberately rather than by default.