I'd imagine that environmental objects can be blocked, except maybe the car slams. I also think that most of those grabs & lasers are blockable. Kabal & Kano's command grabs are blockable. However I think that certain characters should be able to block things that others can't (still thinking about this). Like those barrels, Wind god forbid that they are unlockable, but since some characters have air dashes and such, slug dudes like Grundy should be able to block them. Have you seen his walk speed and his forward dash? Horrendous.
My main concern is the clash system. It looks to be over powered for characters who don't rely on meter that much. Kabal is one of the few characters who doesn't need as much meter as say Quan Chi, Cyrax or Freddy. So he builds meter and can sit on a breaker all day. So if certain characters in Injustice rely less on their meter, they'll be able to always wager the maximum amount to either gain huge amounts of damage on their combos or to nullify yours. I honestly hope they take it out completely. Let the critics whine about this being too much like MK, just give us a breaker.