When I first got my IS-4, I absolutely hated it. It was slow and insufficiently armed. I had a horrible win/loss ratio with it in its stock form. Now that I have all the tech tree upgrades plus a couple of store items, I like it quite a bit. I still want to save up for the IS-7 simply for the increased speed and extra armor. But I won't sell off the IS-4 to get it. I'll save up the $$$$ instead.
As it is now, I can make pretty good money/EXP with it, especially if my side wins or I don't get destroyed. I can usually account for 1-4 kills per game. I'm not sure why everybody says the IS-4 is so completely overpowering. I still bounce AP shells, even with the 130mm. In fact, I even bounced one off an M6! I find myself having to switch to HE to reliably take on JagdTigers and other high armor tanks/TDs. But overall, I find that I like it now that it has been completely upgraded.
As it is now, I can make pretty good money/EXP with it, especially if my side wins or I don't get destroyed. I can usually account for 1-4 kills per game. I'm not sure why everybody says the IS-4 is so completely overpowering. I still bounce AP shells, even with the 130mm. In fact, I even bounced one off an M6! I find myself having to switch to HE to reliably take on JagdTigers and other high armor tanks/TDs. But overall, I find that I like it now that it has been completely upgraded.