Where would you start with mods…. I would think I have over 1000 inc all the islands for the series, of these 500 or so will be arma2 ones, I use around 200 loaded which includes 150ish islands for a2.
Just a couple, out of the box mods worth thinking about to get started...
Sound: 'jsrs', a mix is better, but out of the box this is the best.
Effects; 'blastcore visuals', 'blastcore tracers' & 'jtd fire & smoke'
Ai enhancements: 'ASR ai' (for ace), this is a very particular area and a mix of many is better, but out of the box asr is good. Also 'TPWC suppress' & 'TPWC LOS' & 'st movement'.
Islands: too many to list (over 150), however look below for campaigns, these all include several islands.
Fps boost: 'sap clutter' & 'landtex', these both alter/reduce the clutter on chernarus and also work for other islands
Campaigns that are highly regarded are;
‘I44’ (mp missions/campaign) ww2 mod
‘Namalsk Crisis’ (mp missions/campaign) sci-fi/zombie’esk
‘CWR2’ (mp missions/campaign), cold war era
There are many, BIS forums has a whole section concerning mp missions.
Also: factions, units, vehicles, aircraft, armour, weapons etc.. headache now
All are only imo. but I could go on for ever.. soooo many

