Actually I think Barrier is more of a replacement to Ignite than it is one to Heal - just not one of the 'strictly better' variety. I expect to be seeing it in solo lanes, winning trades and trolling ganks - especially on longer ranged champions who had to think carefully about the choice of Ignite in the first place.

- It gives you the most EHP over time, making it a strong choice for even or disfavourable matchups.
- Short cooldown means you can feel okay about using it for engagements at level 1, because it will be back again by the time you need it in lane.
- Ignite + Barrier is almost strictly better than Ignite + Heal if you can consider dropping Flash on your champion.

If I'm not mistaken, Barrier is still a PG exclusive, not coming over to SR (though it might be nice to see there). As Nome said, it's primarily for melees on PG who need to wade through a fair bit of damage to get at the ranged champions; this isn't nearly as much of an issue on SR, where there's lots of walls and brush for a melee to make use of on their way in, not to mention the simple fact that not everyone is restricted to a single small lane; a melee doesn't need Barrier nearly as much when they're dueling, as opposed to PG where they will almost certainly be exposing themselves to multiple champions.

Does anyone see this as a super nerf to Karthus?