It depends on how much time you want to spend on the project, and what your expectations are. It can be made to look good, for a while, the wild card is how many rotted boards there are. If I were to attack that project the first thing I would do is make sure the screws are sunk below the surface of the boards so they don't tear up sanding belts. Then I would go around putting in more screws where needed. The next step would be sanding until I had a smooth surface, it looks to me like a 1/16" or more would have to be sanded out, and the deep splits, cracks, and checking will still remain. Make sure it is clean and mildew free. Wood fillers don't hold up well to expansion and contraction along with people walking on the deck. Bondo is hit or miss especially on a deck people walk on. All dust must be removed after sanding, if the surface is slightly damp it helps with applying the 'first' coat solid acrylic stain, try and work in shade or on a cloudy day! Regarding finish, I would use a solid acrylic deck stain, no priming, just two coats. Oil based products on a deck are a breeding ground for mold and mildew. It should look decent when done, some might say like a suit on a Gorilla. As I mentioned earlier, it depends on your expectations.
