I was strictly casual PVE for most of Year One. The only time i would consistently run Crucible was if I was working on an exotic bounty.
Now I've started playing more PVP and I'm hooked on the race to get to max rank in Iron Banner and SLR. The weekly bounties and the chance for high end gear help to feed the need.
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Personally I think they're developing these little timed events over the next year or so as testers for content that could possibly come with Destiny 2, if they get positive reactions they'll probably include then permanently. Though I could be completely wrong about it.