Most readers probably like to see their hero win – but not too easily. I’m sure they look for a bit of adversity for their hero – to see him or her show resourcefulness, determination, courage under fire.
In my science fiction stories I have tended to write my heroes as being quite powerful such as Tragathh of the Brell in Soldier of the Brell and Earle, Alien Hunter Class 5 in Alien Hunter, Star Trooper. The former carried with him the residual power of his race as he traveled into the future seeking revenge while the latter had such a diverse range of powers that he was a handful for almost anyone.
While both needed these powers against awesome adversaries, still I think if hero and villain become simply too powerful the reader can lose interest.
In my Marvel Comics fan fiction: http://www.fanfiction.net/u/1276881/David_Scholes
I certainly do write my heroes such as the Asgardian gods Odin and Thor and other Asgardians such as Balder the Brave, Hogun the Grim, and Heimdall as being both more powerful and more cosmically aware than they are written by any current Marvel comics writer. I believe that successive Marvel comic book writers have progressively degraded the power of Earth pantheon gods (such as the Asgardians or the Olympians) relative to the many abstract powers and cosmic entities that Marvel have created over time. In my fan fiction I’ve kept the likes of the skyfathers Odin and Zeus at the power levels they enjoyed in the earlier days of Marvel comics. The so called “Silver Age.” The bulk of the feedback I’ve had suggests that readers like this.
Of course at the opposite end of the scale you can get the hero that is frustratingly, irritatingly weak. I find this considerably more frustrating than the all conquering, all powerful hero.