To be honest the Needler has always been great. The perception of it has changed though. No one would use it in 3 or Reach so I would always grab it and get an automatic few kills. Now everyone wants it.
I like that they just recognized it as heavy ordnance and rolled with it. It's got target seeking needles that explode when they reach critical mass. So they juiced it up to super awesome levels.
In hindsight, embracing it as a power weapon seems like the obvious thing to do.