In CE it was a pretty damn powerful gun. It was a fantastic sheildbreaker and you could pick one up in the blink of an eye. It made completing Legendary a lot easier. It could fire real quick and so was useful for spamming jackals and the like.
In H2 it became infamous in MP as one half of the 'Noob-combo' alowing for easy kills. In the campaign it was still abundant but relativly underpowered, and the overcharge no longer did direct damage but was still extremely useful when completing the game on Legendary. It regular fire mode however was utterly pants.
In H3/ODST it went through some changes, to counteract the 'noob-combo' it's battery was drained whilst holding the overcharge and it's homing ability was greatly reduced however it gained the ability to temporarily disable vehicles and so became more of a niche weapon. It was still useful as a sheildbreaker too however I found it less helpful when completing the game on Legendary. The overcharge still didn't inflict direct health damage but the main fire mode seemed to pack a little more punch.
Finally, in Reach it seems to have picked up a little bit of everything from the previous games: It's regular fire mode pack a bit of a punch but was still unweildly and awkward. Its overcharge was, as always, a moohassive sheildbreaking badass and could disable vehicles whilst retaining the battery drain and reduced tracking ability. It can also cause limited direct damage as well.
In all I think it's a weapon that you pick up as and when you need, it has it's good points and bad points but it still adds something fresh to the gameplay.