People (generally) love superheroes. People (generally) love video games. Yet we hardly see these intersect in a way that is worthwhile. Sure, we get farted out mobile games, but nothing incredibly substantive. I originally had this thought after the huge number of Batman games and the proximity in which these are being released. Solo superhero games are such a rarity, but these characters should get a game of their own.
Superman
There has never really been a good solo Superman game. The games that have been good with Superman are ones that feature him as a playable character, most notably Injustice: Gods Among Us. As much as I bemoan TellTale games though, I really feel like they would make a great Superman game. The big problem with any Superman game has been mechanics, specifically in terms of flying and running. What TellTale lacks in game play, they would make up for in story. Even though I didn't necessarily care for Batman: The TellTale Series, there was still a pretty decent story attached to it. What I would hope for is that after TellTale finishes their Guardians of the Galaxy game, they should potentially work on a Superman game. After this, I would go for a Batman/Superman team up game.
Blade
Werewovles, zombies, and vampires! Oh my! Horror games are on the comeback and this is only a good thing. Blade has been a playable character in lots of Marvel related games, but never has he had a game to call his own. Sure there are some logistical things to sort out: story mode, style, etc. Personally, what I would look for is a third person POV game and being able to cycle between the sword, guns, as well as hand to hand combat.
Hellboy
Resident Evil 7 has shown what horror games can be. Horror games can be pretty damn awesome if they're done properly. Hellboy gets into the paranormal. So imagine demons and other worldly creatures in your face. Since the likelihood of getting a third Hellboy movie is pretty low, Ron Perlman could (and probably would) come back to the character even if it was only in a voice acting capacity.
The Punisher
There really hasn't been as much with The Punisher in terms of gaming. An old SEGA Genesis game, but even in the last fifteen years, there has only been two games. In 2005 to coincide with the release of the film starring Thomas Jane, there was a game developed that took some creative liberties with the universe this was in though. What made this game great was the compelling story mode and user-friendly game play. There was another game in 2009 called The Punisher: No Mercy. Despite the generational upgrade, this game was inferior to its 2005 counterpart. There really wasn't a whole lot to this game. It essentially felt like Call of Duty but with The Punisher characters. There was no personality, no story to it. If you could create a game that has both of these aspects.
Green Arrow
Imagine Green Arrow in an open world. The concept I would work with: the obligatory tutorial level on Lian Yu. Once that is over, Oliver Queen gets rescued and goes back into a story mode for that amount of time. Certainly there would be the open world. Maybe parts could take you to Central City, Coast City, Metropolis, or even Gotham. Granted the story should be centered around Green Arrow, but I see no problem with bringing in other characters.