its around 14.8 gigs, yes I can fly around, the world is pretty big. The flying mechanic is decent(it was a bit better in Superman Returns) and so far I haven't put enough time in to unlock other skills, or Iconic Powers(most of these appear to be available after level 10).
There are heroes and villians, and I picked heroes.
You don't lose your character when you die, you take an 11 second breather, and then you re-spawn in what appears to be a safe zone.
So far, I don't appear to have any special weaknesses, so far I'm dying because I'm getting gang jumped by a lot of Gorrilla's.
I checked out the market place, and you can pay for extra's, like DLC packs like the Green Lantern pack, or Flash pack, and there are other perks you can get, for example you can get options to change character, or have another slot for another character.
The thing I regret isn't putting more time into character creation, I figured I could change my look/clothes later on, but it appears I can't unless I buy that particular perk(looks like it costs 5 bucks), so my character looks pretty plain jane.