They've been trying to ditch Ironside for ages, they tried to dump him when he put up his fee (from the bargain basement prices they paid him for the previous games) for Double Agent, and then they initially didn't hire him at all for Conviction, and only reversed the decision late in the day after the online backlash came. So this has been coming a long time, unfortunately.
I knew there was no chance it would be reversed this time, when I saw that they paid Ironside to appear in a video in order to help 'sell' the transition of a new person in the role. It was smart marketing, especially as it stopped Ironside giving any negative press about the change, as he did when they originally didn't hire him for Conviction.
A potentially even bigger problem is, in my mind, that the new guy just sounds so damn bland, and seems to have very little presence or personality from what I have heard so far. So they didn't even recast with somebody talented, just with somebody cheap. And I think all fans of the franchise deserve far better than that. If you are going to slap us in the face and dump Ironside, you could at least try to get someone else who would try hard to still do the character justice. But here, again just from what I've heard, not so much.
I've been a hardcore Splinter Cell fan since the original game, it's one of my favourite gaming franchises ever, and to me, Ironside is Sam Fisher, so without him in the role I am biased, and I do find it really hard to get interested in this game full stop, even if it is a good game. I'll buy and play it eventually, but every other release in the franchise was a day one purchase for me. This one, I'll get eventually when the prices drop.