Reddit reviews Steelheart (The Reckoners)

I think you would really enjoy Steelheart by Brandon Sanderson.

http://www.amazon.com/Steelheart-The-Reckoners-Brandon-Sanderson/dp/0385743564

Amazon link for easier procurement :)

A few recommendations....

Worm is an amazing fanfic, think Steelheart by Brandon Sanderson except more depressing. It has a slow beginning, but soon becomes awesome.
Synopsis:An introverted teenage girl with an unconventional superpower, Taylor goes out in costume to find escape from a deeply unhappy and frustrated civilian life. Her first attempt at taking down a supervillain sees her mistaken for one, thrusting her into the midst of the local ‘cape’ scene’s politics, unwritten rules, and ambiguous morals. As she risks life and limb, Taylor faces the dilemma of having to do the wrong things for the right reasons.

Lily and the Art of Being Sisyphus is hilarious and absurdist, a bit like Terry Pratchet. Still updating every two weeks.
Synopsis: Lily is not quite a normal little girl. The Dursleys always say she's a freak just like her freakish parents, her uncle Death seems to be convinced she's the grim reaper, and her ever political and invisible best friend Wizard Lenin just thinks she should take over the world. On top of all that the secret society of wizards think she's Jesus. AU female!Harry among other things.

Saga of Soul is Puella Magi Madoka Magica meets science. Slow to update though...
Synopsis: Meet Eriko, an introverted, intellectual teenage girl with good intentions. Now, watch Eriko get caught in the middle of multiple simultaneous plots as fairies, demons, inter-dimensional empires, evil geniuses, immortal killers, cosmic horrors and more all make their move, and it's up to her to save the day."Saga of Soul" tells the story of Eriko, A.K.A. Soul, as she strives to protect the world against all odds. Updated on an irregular basis.

Imperfect Metamorphosis Takerfoxx took a scrapped character from Touhou and made them an vengeful abomination bent on killing and absorbing everyone into their eldritch body.

To the Stars I guess this is like Star trek meets Puella Magi Madoka Magica? It's completely different from the source material, the world created is immense.
Synopsis:Kyubey promised that humanity will reach the stars one day. The Incubator tactfully refrained from saying too much about what they would find there.

Gods & Monsters God character development (or should I say character regression?) If you like broken characters trying to do the right thing, take a look.
Synopsis: Miranda struggles to keep a fractured Jane Shepard focused on the task of defeating the Collectors. Meanwhile, Maya Brooks steals Shepard's clone and tries to stay one step ahead of Cerberus. Pairings: It's complicated.

Legend of the Sun knight It's not a fanfic, but a fan translation of a popular Taiwanese novel. Gods cannot walk the earth, so they choose human representatives who are supposed to be perfect. The Sun knight is supposed to be the living carnation of justice and compassion; however he has megalomaniac tendencies...

Edit: added in synopsis

Another amazing Brandon Sanderson book is Steelheart.

Basically, some people get superpowers, but it doesn't work out so well.

http://www.amazon.com/dp/0385743564/?tag=googhydr-20&hvadid=43975918203&hvpos=1t1&hvexid=&hvnetw=g&hvrand=780631542628712137&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_6z31kqll2z_b

Steelheart by Brandon Sanderson is similar to what you're asking for.

Edit: though, maybe it's more about role reversal than ambiguity. Either way, it's a good read and it isn't too long.

If you are looking for something fun, try Steelheart by Brandon Sanderson. Basic premise is that some macguffin starts causing people to develop superpowers. The twist is that everyone who does ends up being a villain. The protagonist is a regular guy that tries to fight the Epics (as the super powered villains are called). It is the first of a series.

I have quite a few on my wishlist, Can we put more than one? One, two, three, Four, five & six. I love books and couldn't decide on just one lol.

http://www.amazon.com/Steelheart-The-Reckoners-Brandon-Sanderson/dp/0385743564