What makes a good futuristic romance hero? In my opinion, the exact same things that make a good romance hero, period. Of course, these are just guidelines and made to be broken.
The hero has a code of honor
It might not match society's idea of honor, but he strives to always live up to his own code.
Since my heroes have all been military or paramilitary, they tend to adhere to the normal social ideal of honor. However, in The Skypirate Justine Davis creates a hero who attacks coalition shipping. This is definitely not considered a good thing by the powers that be, but the coalition is a corrupt entity and by attacking it, the hero feels he's striking a blow for the planets that were overtaken by this imperial power.
We also see a lot of a personal code of honor in vampire books. The hero either only takes enough blood to live on, leaving the donor with a pleasurable interlude or, if he kills his prey, it's always the dregs of society, the kind of bad guys that few readers will feel any remorse over. If the vampire loses his control and accidentally kills an innocent, he's been tortured by this from the day it happened--even if it's been hundreds of years. I can't think of one instance where a vampire hero in a romance has killed someone "undeserving" for regular feeding.
Heroes are protective and reliable
These men might be as alpha as all get out, but they'll die to protect someone they perceive as weaker than they are--even if it's with great reluctance--and the heroine can rely on him to help her no matter what the circumstances.
I've noticed a pattern in my books. No matter what else is going on around them, the hero and heroine are always a team, able to rely on each other one hundred percent. They might not trust each other, in fact, in Through a Crimson Veil, Conor was damn pissed off at Mika for the lies she told, but despite all that, he continued to protect her and Mika knew he'd never let anything happen to her.
Heroes are self-reliant
They don't whine to others, they take care of their own problems.
In Janice Tarantino's The Crystal Prophecy, not only is the hero self-reliant, surviving a situation that felled other lords around him, he also is able to shoulder the burden placed on him by The Widows and take the steps necessary to save their society.
Heroes have an emotional vulnerability
No matter how tough they are, they need love.
I tend to write heroes who are loners, with few connections to others (Eternal Nights is the one exception) and this is part of the emotional vulnerability. We all know these guys need to be loved. The most extreme example in my writing is Conor from Through a Crimson Veil. Through no fault of his own, he was rejected by his mother--she refused to even touch him if she could help it--and to protect himself emotionally, he built a fortress around himself. Then Mika comes along and tells him she loves him--often. He wants to believe, but he doesn't quite dare. In the course of the book, Conor inches forward toward trusting and believing that he really is worthy of love.
The difference between regular heroes and futuristic romance heroes
IMO, the main difference is the futuristic hero can be larger than life beyond what most authors can do with a contemporary hero. Sure, he can be a galactic police officer, but he can also be Prince of Planet X, out to save the galaxy from the evil empire.
But whether he's a futuristic rebel out to topple a corrupt totalitarian government or a contemporary hero who's out to catch a murderer, the reader has to care about the character.