Now that I've been through numerous of dungeons above +10 difficulty, I can safely say what I was thinking about at the first dungeon I did with this affix: This is by far my most hated affix as it is right now.
This affix's design is interesting and I think it's a good idea to have an affix which tests the players' abilities in high priority target switch. However this is not what the affix is doing most of the time. If there's 2 or less targets, the affix does almost nothing. Seldom a ball spawns next to the boss and one melee swing is enough to take care of it and you're good for the next half a minute or so. This affix shines at 3-6 targets when a couple balls spawn often enough to make this an affix you should keep an eye on and deal with accordingly, but they still spawn rarely enough so there's room for everyone to do their normal dps/tanking duties.
After a pack size of 8 the shit starts to hit the fan. You pretty much have to dedicate one player for the orbs alone and the other two can focus on dpsing the pack whilst helping with orbs how they can.
But it's not the KILLING of the orbs that is difficult, it's simply TARGETING enough of them in the middle of the nameplate jungle that makes this test a player's capabilities of choosing the right nameplate instead of high priority target switch capabilities. What this does is that this affix single handedly stops your group from pulling any pack bigger than 10, which is already pushing it, simply because it will be faster to pull less and have less orbs to deal with at once.
TL;DR Explosive affix goes from 0 to 100 way too fast in terms of difficulty when the size of the pull grows and tests player's abilities in choosing the right nameplate instead of high priority target switch. A strategy of a dedicated orb destroyer is adviced during high pulls, which is annoying.
Edit: This needs to be gaining more attention so I need to clear something up. It's okay to have affixes that are slightly more difficult than others and especially affixes that favor some classes while some classes might struggle. For example spriests are having a very easy time during skittish weeks where most melees are struggling. During volcanic weeks again melees have it easier while spriests have to be on the move dodging stuff.
The affixes should still be somewhat balanced between each other. If not, what we get are events like the great tank m+ boycott that happened during skittish weeks.