Some of the live versions on Unleashed are really good. The Sad Wings material especially comes to life here. It's nice to have some "definitive" versions of these songs. The Sin After Sin and Stained Class material is good too. The guitars sound a lot fuller and, consequently, the songs sound heavier. The decision to leave off so much of the Killing Machine material is mind-boggling, especially considering Hell Bent For Leather, in particular, became a live staple. It'd be like if Maiden left Run To the Hills off Live After Death. That being said, I'm not sure what I'd take off the main album. It's a strong set of songs. I suppose this should've been a double.
I don't really consider Priest a live band in the same way as, say, Iron Maiden or Iced Earth. I enjoy seeing them live and listening to the live recordings, but it's very rare that I deviate from the studio albums. However, you could make the argument that the definitive Priest was born with Killing Machine. They found their sound during this time. So having live recordings of older songs to fit the new sound and image makes sense. Like I said earlier, these are the definitive versions of some of these songs.
If I were to give the album any criticism, it's that it doesn't really feel like a live album. Save for a few songs, the crowd seems nonexistent and there's no interaction with the audience. It just sounds like a raw performance in the studio (which it very well could be I suppose, at least we know the vocals were redone). The song list also doesn't really have that live concert flow. Exciter and Running Wild is a good 1 - 2 punch, but after that, it seems like a random slab of songs. Ending the concert with Tyrant also just seems really anticlimactic. You could make the argument that it's hard to replicate the flow of a live concert when confined to a single LP, but to that, I would submit Cheap Trick's At Budokan which was released a year earlier. That album excels where Unleashed falls short.