Either Tabletop D&D or Warhammer 40k. I personally like the combat system in 40k better, but D&D is easier to understand, not to mention is a lot more recognizable. Although the setting in 40k is a lot more in-depth and complex. Actually, yeah, I think I'd have to go with Warhammer 40k Tabletop Roleplay. What? I didn't hear anyone say it had to be a video game, and Tabletop games are legitimately awesome. Completely wide open sandbox, hundreds of hours of playability, not to mention that you can do literally anything reasonable for your character, so there's no issues with limitations of controls. I mean, in my first ever Dark Heresy Warhammer 40k Campaign, I started out as a lowly guardsmen from a feral world that was kidnapped, given a gun, and expected to fight; and by the end I had a flying Motorcycle, Giant Las-Cannons and Machine Rocket launchers, chainswords, psyblades, and so on. not to mention that I was strong enough to throw an elephant at people as a legitimate attack.
Throughout that one campaign I did everything from Jumping of cliffs hundreds of feet high after shooting off a man's leg from 100 meters away, Helped with orbital bombardment on a planet, opened a door with a gunhammer (killing 3 people in the process), coming back from a successful suicide mission via flying motorcycle, pulling out a pair of sunglasses from the warp in order to look cooler while coming back from said suicide mission, killing a fighter drone with a flintlock pistol while attempting to get back from a certain suicide mission, lassoing a servitor with some rope I happened to have on me while I was flying through space after a suicide mission. (It was a busy day for me) There was even some slower economic based challenges like building a factory to provide supplies and profit, rallying a city to come to our aid, and even building a combination hotel/casino/restaurant/massage parlor/something else. Hell, there was even a stealth element to it. Despite my large stature and heavily armed nature, I snuck into a fancy dinner party completely inconspicuously. I simply learned how to cook some basic meals in the weeks leading up to the party. Then I caught a massive shark that the DM might've expected me to use as a signature dish, which I did, but I also used it to smuggle in a lot of my weapons, and even one of my teammates as well. And I never once broke the rules of the game.
I'll admit that the single-player is non-existant, and you usually want a group of at least 4 people to play with, but I got almost 200 hours out of that single campaign, and there wasn't any farming or grinding, or any other repetitive annoying stuff. Oh, and at one point I built a gun that fired Shurikens and Lightning. Then I mounted it to Flaming Chainsaw Gun-chucks.
When you say "best visuals", while the design and aesthetic are (near enough) second-to-none, the 3D graphics themselves haven't really held up that well... Don't get me wrong, they don't detract from the game - and I have quite nostalgic feelings regarding them - but they might put off new players a little, which is a shame. A lot of "early-days 3D" games are similar :/
