Operation Flashpoint (for anyone who bought it on release back in the day).

It was later turned into the Arma series and re-released with this name to fit the series branding.

I've played them all - this was the best of the lot IMHO.

I think Bohemia parted ways with their publisher Codemasters, who retained the Operation Flashpoint trademark.

I'm a bit sad they never managed to make an equally enjoyable campaign in any of the later installments.

Multiplayer is nice for others I guess, but not really for me.

IMHO the ARMA3 campaign is quite alright (once you realize how much freedom you have between the missions), also the Contact DLC was pretty great IMHO.

But where ARMA3 really shines is single-player sandbox mods like DUWS-X.

Judging from steam comments, seems like that creator passed away recently. RIP