I knew a few people who suggested rowing was a great workout and you wouldn't need anything else. Is it really? It seems pretty tame and I cant imagine you don't have to do anything else.
Getting on a rowing machine is pretty tough man. It's about endurance, and it worked most of the muscles in your body. You're gonna be super sore after your first session on it. But it'll get you in shape pretty quick if you stick with it.
It's good mainly for cardio and endurance. You hit your back and biceps and a bit of legs and core, but I wouldn't say it completely replaces all other workouts. You'll miss out on progressively overloading with weights as well as other muscles that aren't in use.