It's being called tired because it just feels like that, the game really lacks unique identity of what makes it stand out. Besides the overuse of zombies in things, the setting also is typical zombie fiction tropes, the lead character has a very "normal dude" look. What exactly is the hook of the game? The reveal of the game was nothing but video of the main character running from a giant horde of zombies and shooting hundreds of rounds at them with unlimited ammo... not exactly riveting stuff.
Story wise, visual wise, etc.... the game just lacks any real hooks in everything it does. The game looks like from the more detailed previews, but the game lacks any identity to set it apart sadly.
Take Last of Us, many were calling it just another zombie game, but we got a heavy focus on the 2 character story elements that really set it apart. Lot of focus on narrative throughout the games previews and presentations. While Days Gone we just got this random dude who is going around an open world to do fetch tasks? I guess? It's hard to say but it looks like typical open world gather a thon.