With respect to my colleague, Doc Brown, I disagree. Some of the only jurisprudence we have about using artwork under a copyleft licence as part of a greater work comes from Drauglis v. Kappa Map Group. Although the copyleft content in Drauglis was under CC-BY-SA, not GPL, I believe the analysis applies because the question of what constitutes a derivative is a copyright question, not a licence-specific one.
In this case, the court found that not only was the whole work (a road atlas) not a derivative of the CC-BY-SA cover photo, even the cover image was only a collective work, not a derivative one.
Though that case isn't a binding authority in any jurisdiction, given that you're not modifying the artwork the analysis seems germane, and suggests that you could use the artwork taken from the GPL source game without having to GPL your entire game. You would need to honour the terms of the GPL with respect to the artwork, though. And, of course, IANAL/IANYL, so you would do well to take qualified legal advice before relying heavily on this.