I can't believe I'm saying this to the master of gravity, but I disagree with your comment about gravity shield :p That is a very effective shield, particularly in PvE, though it suffers somewhat in PvP due to the prevalence of rush decks there.
On the topic of this new shield, I really like the idea. It's costed appropriately, and gives a useful, but not overpowered, secondary effect in reducing direct damage dealt to the player.
As for the part about asking whether the damage is dealt in increments or in one bunch, it doesn't really matter because that's probably extremely easy to change in code if this shield or something like it ever made it into the game. I've done a bit of programming, and the part of the code that deals with that is probably smaller than the length of my post.
First of all, I'm not the Master of Gravity, as you can see :S
According to your logic, Reflective Shield is a very effective shield because it perfectly/decently counters spell decks such as UG, pestal, or fire stall. However,
still has two other shields that can be used in a variety of situations. Same goes with most other elements with percent blocking or direct damage reduction shields. Gravity doesn't have an all-purpose shield, and thus I'm emphasizing the necessity of a decent shield.
Also, when I talk about effectiveness of a card, I almost always talk in terms of PvP. In the current metagames, we don't even need to discuss cards such as gravity shield since we have the imba Shard of Sacrifice. <_<
And moomoose thanks for the image. I just enlarged the shield part. Decided to stick with the name, though.