I know a couple of things about Queensryche. I'll say this -- Todd is a good singer. His voice is very suited to sing the old stuff -- EP-Rage for Order. After that though, particularly as you get to Empire, you can start to see where he's not as strong. His voice isn't as rich and powerful as Tate's on the "warmer" Queensryche material. One listen to jet city, lucidity,another rainy night, or even damaged (which is a personal fav), you can tell. But for what Queensryche is doing now, Todd is solid.
He has really improved on the last couple of tours. He's learned to become a professional singer, as opposed to a guy who goes out and wails, and if the voice isn't there, he's in trouble. Now, he doesn't go for all the notes -- he picks specific ones -- and he cuts notes off a little to save his voice.
As for Tate -- the guy has lost his mind, and is realizing now he's pretty much done without Queensryche. But you can't deny the man was one of the three principal architects of Queensryche's sound (along with DeGarmo and Wilton). The man had a legendary voice from 1981-2005 (anyone who heard him on the summer 2005 tour with Judas Priest can't deny how good he sounded, even if they had to drop things a half step). Tate's operatic voice, progressive rock leanings, and dramatic delivery meshed with DeGarmo's keen sense of melody, chord progressions, and harmonies, along with Wilton's push for heavy riffs, defined Queensryche through the band's original tenure, and the brief handful of songs on Tribe. Queensryche would not be Queensryche without those three (and honestly, all five, the rhythm section of Jackson and Rockenfield is underrated). And trying to minimize Tate's impact on their sound (which admittedly, I did a bit during the lawsuit of 2012) is foolhardy.
If Tate ever did rejoin (and I never say never, but I don't think it would be until 2018-2020, honestly) he'd have to be publicly apologetic to his bandmates for attacking them and trying to steal money from underneath them. And Tate, while he laments not being able to "work things out" with QR, has not yet even acknowledged his wrongdoing. So there's a long way to go. But without DeGarmo being a part of it (and I think it is very telling he's stayed far away from La Torre-fronted QR -- I'm pretty sure he knows TLT isn't the same kind of talent Tate was and is keeping his distance until all options for full reunion are extinguished), I'm not really interested in Tate returning.
For those that love the TLT-fronted version of QR, it's a good time. They have two pretty good albums, and hopefully, this next one will be great. But for me personally, I have some legit hangups (both musically and personal) that have me not as impressed with them as I originally was. The original Queensryche was something special. This lineup (like the DeGarmo-less, Tate-fronted lineups from 1999-2001 and 2003-2012) is just a different animal, and not as good.