Naughty Dog's 2015 PlayStation 4 game Uncharted 4: A Thief's End is aiming to be the "ultimate Uncharted" experience, according to co-director Bruce Straley. In a new interview with Game Informer, Straley explained that making games is no walk in the park, and said pushing things forward and evolving the Uncharted formula is Naughty Dog's overall goal for the project.

"Making Uncharted 4 is hard. Making every game is really hard. It's never easy," Straley said. "Where's the blueprint? Who's got the f**king blueprint to make these things?"

"We're constantly questioning how to do this better. We're driven by … we want to create an experience that resonates with the player, and what we're trying to do is create amazingly rich characters and an adventure that these characters can go on," he added. "All these things have to make sense and they have to click together with the controller in your hand. And I want to feel engaged."

Straley went on to say that Naughty Dog's learnings on 2013's The Last of Us will help drive more innovation for A Thief's End.

"I don't want to just play the same game as I've always played before. So we're going to evolve it," he said. "And then we did The Last of Us and that gave us new concepts about how to evolve things. Each time, it's not like as developers we're like, 'I'm bored.' We as players, we want to play a game that is the ultimate Uncharted that we think this thing could be. It has such great potential."

"We as players, we want to play a game that is the ultimate Uncharted that we think this thing could be" -- Bruce Straley

A Thief's End's other director, Neil Druckmann, added: "This is the Uncharted we feel like we want to make and the culmination of everything we've learned on Uncharted and The Last of Us."

In terms of gameplay, as we saw in the game's demo from PlayStation Experience last month, A Thief's End will offer a "wider, more sandbox feel," according to Naughty Dog. There's even a new rope and grappling hook mechanic that Nathan Drake can use to swing from one location to the next, bringing about an on-command traversal option not seen in earlier games.

Also in the interview, Straley touched on the overall tone for A Thief's End, stressing that, while the game will have some intimate, personal moments, it will still be a lighthearted romp.

"We're not gonna make it too dark, everybody calm down. Just take a breath," Straley said. "We're retaining the lightheartedness; it's Nathan Drake."

A Thief's End launches later this year, exclusively for PS4. For more, check out GameSpot's previous coverage.