Gun is far from groundbreaking but at least it does what it does and it does it well.
The story in Gun is actually pretty cool. You start off with your father and end up on a steamboat where some mysterious stuff happens and then the boat is attacked. Then some other stuff happens and it turns out you're on a quest to find an artifact...but so is this big bad Magruder fella. That about sums it up quickly, but there is more to it than that. Aside from the main quest there are a TON of little side missions to do, which vary from bounty hunting, law enforcing, pony express, hunting, gold digging and gambling. All are great distractions from the main story and do help lengthen the experience if you decide to do all of them.
The world of Gun is pretty large, but not so large that you'll be lost most of the time. There are distinct parts of the world and you can travel through most of them by following the train tracks. Horseback riding is a must in this game since your character walks like he's on a skating rink....in slow motion...especially if he's drawn a weapon. But the side missions will have you traveling all over the place and you get familiar pretty quickly.
The weapons are standard; rifle, pistol, shotgun, bow and sniper. Nothing spectacular, even when you upgrade. The main differences are in how much ammo each stores before you have to reload, with the exception of the bows, which each pack a different punch. You can also buy upgraded stats for your guns from the storekeeps. The best addition to Gun is it's version of "bullet time" which slows time down and allows you to take out everyone in a super quick fashion. It works quite well with a flick-to enemy sight and you can still fine tune the aim to get the glorious headshots. It isn't solely a gimmick, either, it is necessary to advance in certain situations and it certainly helps out a lot in others.
Controls are kinda not so great, especially when you're amid action. The L and RB buttons are used a lot, but I would accidently hit them instead of the triggers and vice versa, which doesn't help things much. Camera can get kinda jumpy too in certain situations, but you never have to do any platforming, so it isn't a huge distraction.
Sound is one of the best things about the game. There are great cutscenes with some great dialogue. The guns, environments, etc all sound pretty great too. I found myself skipping most of the side mission dialogue because it was unecessary, but it was still nice to have, even if I didn't hear it.
The story is branched out through very cinematic cutscenes that do a terrific job of captivating your attention. If Gun was a movie, it would be a great one...and about the right length, too...The game is solely a rental, as you could probably be 100% done with it in under 10 hours...And then there's no real reason to keep coming back.
It's fun while it lasts, but there are some trial and error to the missions and the last boss is staggeringly difficult, especially considering the game itself is pretty easy. Overall, Gun is not the videogame equivalent of Deadwood by any means, but it doesn't disappoint.