Maybe it's just me, but I'm not really a fan of having World Cup games decided by PKs.
In the NHL regular season, tied games go to OT, then if still tied, to a shootout (penalty shots). But in the playoffs, they just keep playing until someone scores—no shootouts. Which I think makes sense, because regular-season games you just want to get through, but playoff games are obviously more meaningful, so they have an "actual" ending, as opposed to the sort of (IMO) "artificial" ending of the shootout.
I'd kinda like to see World Cup games switch from PKs to sudden-death OT. I think that would be a more organic way to end games.