Been playing Arma Reforger for the past few days. The game is fairly bare-bones in terms of content, and has huge multiplayer stability problems, but when it's working it has to be one of the most immersive games ever made in my opinion.
The new engine is a big upgrade over the last in terms of graphics, physics and controls, and almost every item you interact with in-game will have a corresponding animation. The main 'Conflict' mode which is a PVPVE game mode was really slow at first, but after people are figuring out how it works now it's really starting to grow on me.
In a bit of time, with some more weapons or vehicles added in by BI or by modders, and with the multiplayer issues fixed up, this game will be well worth it even just to keep you going until ArmA4.