I played quite a bit of #HaloInfiniteSeason4 and it doesn't seem to be a huge difference. There's infection mode and a few new levels. The jungle level (sorry forget the name) is cool but it struggles to get up to 120FPS, on my Xbox it is peaking at 120 but dipping to 106-ish regularly. #gaming
As for the state of the game, I don't think Series 4 will attract many new people. The population is what it is, we won't see many new people joining this game.
Still, I enjoy it :)