Thus styled with the dot for copyright reasons (it was definitely not not a video game revival of the old US TV show), Gunsmoke hit the arcades at roughly the same time as the fondly remembered Commando, and the premise is basically the same. Guide your guy up the screen and blow the baddies away. There are a couple of key differences apart from the theme - one is the presence of end-of-level bosses in Gunsmoke, and a significant change in the control scheme, of which more shortly.
When it made its way over to the humble NES in 1988, Capcom made a number of small changes for the home. It was pared down a bit (the number of bosses were cut down), power-ups were introduced and could be purchased from in-game shops, and meeting the big bad at the end of the level required the acquisition of a wanted poster - a "neat" little trick that meant levels had to be played over and over until one was either acquired or purchased from the store. Interestingly, the localisation work was done by someone with a sense of humour as well. Plot-wise, you're up against a gang of varmints called The Wingates. They've taken over the town of Hicksville (yes, really) and you, their saviour, trades under the name Billy Bob. Brilliant.
Readers know I have an interest in extinct play mechanics that never caught on. As mentioned earlier, Billy Bob faces straight up the screen. His saving grace is button A shoots diagonal right, B diagonal left, and both together fires dead ahead. It's second nature once you get used to it, but it a massive pain confronting enemies behind you. At least in Commando and its sequel, Mercs Capcom realised that was quite a handy thing to do. Therefore, unsurprisingly, despite not being game-breaking this sort of control method slipped into obscurity with the title that carried it.
As such, while not a common title Gunsmoke isn't horrendously expensive. As a venture into a path of gaming conventions, it's a not unpleasant stroll.