A Destroy All Humans! remake was recently announced by THQ Nordic, and it will stay true to the original game in many ways. However, it will have some quality of life improvements that were added in sequels, improved graphics, and apparently a little bit more content than what was delivered in the original release.
The Amazon listing for Destroy All Humans! promises a long lost Area 52 mission, plus the game's development director at Black Forest Games has said that it will be much longer than the original. Speaking to VentureBeat, Onurhan Karaagacli said, "It should be at least 30 or 40 [hours], but I wouldn’t quote me on that quite yet. It’s not a short game at all, though. We’re hoping to add a lot of replayability with the open world component. You have challenges. You have upgrades. You might want to destroy stuff with the UFO, or you might want to destroy stuff on foot."
The original Destroy All Humans! only takes about 10 hours to beat on average, and less than 20 hours to 100% according to playtime aggregate website How Long to Beat. It's possible that Karaagacli is just overestimating how long the game will take to complete, or it seems whatever is being added to the remake will genuinely add some extra time to the experience.
For the most part, the Destroy All Humans! remake is exactly like the original in terms of plot and mission structure. The game is even retaining the original voice acting instead of recording new lines, and it is expected to basically play like an copy of the 2005 game, albeit with those quality of life improvements, the new mission, and prettier graphics.
Whether or not there is enough new content in Destroy All Humans! to boost its playtime as much as Karaagacli has said remains to be seen. However, more details on the game should come to light in the months leading up to its 2020 release date.
Destroy All Humans! is in development for PC, PS4, and Xbox One for a 2020 release.