The closest thing to playing as Christian Bale's Batman in GTA would probably be Netherrealm's rendition of Batman from Warner Bros. Injustice: Gods Among Us. Well, if you didn't already know, Batman from Injustice is now fully playable in GTA IV.
You know what's really awesome? The fact that they have the Tumbler from Nolan's Batman trilogy in the video as well and actually managed to get the same “gritty” look as the movies. Combining this high-tech Batman with the Tumbler and then mounting up the LCPD mod, you could literally play Grand Theft Auto IV like a vehicle-based version of Batman: Arkham City, going around town and fighting crime.
While the style of this mod is truly noteworthy, I don't think it surpasses the fun-factors associated with the Iron Man mods. I'm sorry, but seeing Iron Man fly around battling people and using those nifty weapons and all that jazz is just really cool.
Still, the modding community is just taking GTA IV to all new heights, showcasing so much great potential for Rockstar's formidable open-world action title, like the Back to the Future time traveling mod. It's funny because even without actual marketing promotion, Grand Theft Auto still markets itself.
You can also check out the latest screenshots for GTA V if you need a fix to hold you over until the sequel launches this fall.
If you'd like to get all gritty and add the Dark Knight to your GTA, you can do so by visiting the GTA 4 Mods website.