I doubt many people would have been clamoring for Bryan Cranston if he'd never shaved his head for Breaking Bad.
This is because many people just want someone who looks like the character, acting prowess be damned. (See: Everyone who complained about Hugh Jackman's casting as Wolverine, instead crying for Glenn fucking Danzig.)
Anyway, Mark Zuckerberg as Lex Luthor is pretty nifty. I'm hit and miss on Snyder as a director (love Watchmen
and Dawn of the Dead
, I thought Man of Steel
was very well directed but needed a better script, couldn't get into 300
and Sucker Punch
is just appalling), but with very few exceptions -- Malin Åkerman was atrocious in Watchmen
, and honestly Cavill has a disturbing lack of charisma -- Snyder's casting is generally spot-on. At the very least, he's very good at picking actors who match his vision for the character.