If there's one thing at E3 that's made me feel like we may have crossed a technological threshold this year – that soon, we're going to be able to play games that weren't possible on the current generation of hardware, games that are really different rather than just prettier – it's The Witcher 3

“ This one island, Ard Skellig, is evidently bigger than the entirety of The Witcher 2's world.

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“ The weather and lighting transform the scenery - rain and wind buffet the grass, and at night forests look denser and more ominous.

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“ I'm more impressed with The Witcher 3 than anything else I've seen at E3.

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The Witcher 3 opens the Witcher story on a new, blank page. The maleficent, petty kings that Geralt worked with or against in previous games are gone, their kingdoms collapsed. His quest this time is more personal, and you don't have to have played the previous two games to understand what it's about. As the former kingdoms are mired in chaos, a dark force called the Wild Hunt arises; like Game of Thrones' White Walkers, they have lain dormant for long enough to have passed into myths and nightmares.Visually, they are more like Lord of the Ring's ringwraiths in black, spiked armour, sailing through the air in clawed ships of obsidian bone, killing and burning in their wake. The demo begins as Geralt – sporting a rugged new beard - sets out to find the lone survivor of one Wild Hunt attack, a man who lost his daughter along with every other person in his village when their ship appeared out of the night.This one island, Ard Skellig, is evidently bigger than the entirety of The Witcher 2's world. As Geralt stands on the edge of the cliff you can see far, far into the distance. He boards a pulley-powered wooden platform that takes him down the side of the mountain to the coastline below, and I saw boats leaving the harbour for the sea, oars driving through the waves, and stone buildings hewn out of the mountainside. At the harbour, fishermen are working. After walking along the harbour, Geralt boards a boat of his own and sets out for another island – when he gets out to open sea, a whale's tail emerges from the deep and slaps against the surface of the water. On a stormy day, our demonstrator says, the small craft would be dashed against the rocks, making boat travel ill-advised. All of this is totally seamless. There's no loading at all.Out in the wilds, you'll come across things that you can choose to investigate, or not. It's not like Bethesda's world, where new locations are often mini-dungeons that you can enter; everything lives on the map itself. You can see settlements, lone buildings, ruins, forests and plenty else off the paths, feeding the impulse to explore. The Witcher 3 doesn't do quest markers, at least not right now. CD Projekt Red wants players to be driven by their own inquisitiveness. With such a huge map, it needs to be well-populated with things to do; our demonstrator explains that there will be a combination of random events and plentiful written side-stories to take part in.Hunting is a much bigger part of The Witcher 3 than in any other game in the series. Like in Dragon's Dogma, huge boss-sized beasts roam the map. One such creature, which looks like an overgrown, carnivorous stag with towering antlers and slavering, bloodstained maw, lurks in some ruins that Geralt passes. He lures it out into the open, where there's more space to evade its charges. It's a magic beast that can hypnotise Geralt, darkening his visionThe stag-beast retreats to its lair, giving Geralt a chance to catch his breath. At this point, our demonstrator says, you could track the beast down and finish it off, but he moves on instead, fast-travelling to a village on another island. As Geralt meditates by a campfire, we get the opportunity to see The Witcher 3's day-night and weather systems at work. The climate and lighting transform the scenery around Geralt – soon rain and wind buffet the trees and grass, and at night the forests look denser and more ominous. Weather will affect monsters, too. On a full moon, for instance, wolves will be more aggressive.At the village ,we move on to a quest that shows off The Witcher's moral ambiguity and black humour. A village has seen several killings lately, with dead men found tangled in roots. The religious village elders believe it to be the work of a forest spirit, where Geralt (and the younger inhabitants) know it to be the work of a monster. For a price, Geralt offers to track it down – but first he must deal with the villagers' antagonism.Heading out into the woods to find the monster, Geralt uses Witcher senses to track it down. Tracks, dead animals and other clues show up in red in the woods, and once you've found enough evidence you can figure out what the monster is and how to fight it. This isn't a cute optional extra; there are many, many monsters in The Witcher 3, and without knowing how to fight them you'll get slayed. The forest beast turns out to be a Leshen – a creature of bark and bone, like a violent Ent with the skull of a dead stag. It stands “tall as a towering man”, informs the bestiary, next to an intimidating-looking illustration of the creature.But there's always a twist in The Witcher, and there's rarely a right answer. After killing the Leshen and returning to the village, Geralt discovers that the young men have killed the elders in his absence, accusing them of colluding with the beast. As a consequence the village later descends into anarchy, and outlives the beast by only three months. In the demo we get this information in a flash-forward once the quest is complete, but in the full game you won't know the consequences of your actions until hours and hours after the fact, perhaps when you happen to return to the area again.By this point I'm more impressed with The Witcher 3 than anything else I've seen at E3. The game was running on a PC the size of a Shetland pony, and the graphics are nowhere near final quality, but it still looks stunning. It'll be coming to Xbox One and PlayStation 4 as well when it launches next year.On this evidence, nothing comes close in fantasy RPGs right now. The Witcher 3 incorporates the best aspects of games like Skyrim, Dragon's Dogma and even a touch of Dark Souls, as well as all the strengths of its predecessors. It's huge, stunning to look at, truly open-world and open-ended, and phenomenally detailed, with the same sharp, characterful writing that elevated the first two Witcher games above all their contemporaries. This, for me, is what next generation really means. I cannot wait to see more of it.

Keza MacDonald is in charge of IGN's games coverage in the UK. You can follow her on IGN and Twitter