Ok, the ISU-122S is completely silly.
Same gun as the SU-122-44 except, wait, even MORE DPM (and the DPM on the SU-122-44 was already ridiculous). Sure, it has less armor (actually it has better armor on the sides and same on the front but it is less sloped). It is also less maneuverable. However, weirdly, it is still decently fast. From a stop it takes a minute to get going but from medium to stop speed it accelerates at a decent clip.
I played two games in it, in my hotel, where I have frequent lag spikes that freeze me up for 2-3 seconds.
First game: 3.5k damage, 7 kills, Mastery.
Second game: 2.5k damage, 4 kills, 1st class. Would have gotten over 3k easily but I had a 6 second lag spike against a T29 and when I came back I was running into a building facing the wrong way so he killed me.
Comes with a crew that is like a girl crew so free BIA that doesn't count against skills.
It's basically an SU-152 except a lot better armor and maneuverability.