I haven't played Splinter Cell, so I'd say get Just Cause.
You can spend hours and hours grappling around without completing a single mission and have all the entertainment you need.
The reason I say this is because the voice acting is shit, and the stronghold missions get really repettetive...
Other than that, there are craptons of vehicles, airplanes, choppers, boats, and stuff to grapple to other stuff...
Yeah...