With the ArmA III alpha released currently and the game set to fully release later this year, these old instalments may be forgotten easily. But that doesn't mean they're bad by any chance, yet that doesn't mean they come without bearing faults.
Optimization: The MilSim's optimization gives worry to players about how ArmA III's optimization will be, come final release. There are tweaks to apply to the game and they work like a charm. But it would be nice to get a higher frame rate as default and use these tweaks so you don't drop under anything unplayable.
Story: As most of us know, the campaigns we got in ArmA II and OA weren't that great and some missions included were burdened with buggy AI. Thankfully the game didn't 'hand-hold' you through each mission. Making the campaign last quite long as you didn't know what to do sometimes as you have the whole map in your hands with tasks filled around it so you didn't know where to start. I doubt some people jumped in to the campaign after hearing many peoples problems with it. It isn't a major fault with the game, but some missions could be created in the in-game editor in the matter of a few hours.
Modding: The game has dozens of mods available and the game can be modded easily with mod folders, steam has no problems with mods and once the folders are in the game's root directory all you have to do is go to set launch options in steam and type this: "-mod=@modnamehere" and it's active! Mods range from skins for infantry, to new weapons, vehicles and maps! Some completely change the game for the better. This is great as without mods, I believe people may have tired of this game much more quickly than it is needed.
Editor: That brings me to the editor. The editor doesn't include any basic tutorial to get you started, it doesn't include a tutorial for it at all! Don't worry though since many people have created many tutorials (basic and advanced) to help you get started. Creating missions doesn't happen as easy with those tutorials. For advanced mission makers and some beginners that want to dig a little deeper, you will have to learn some scripting for creating task and briefings for your missions. I made a full mission after some time of learning and it took me a day and a half. It was fun to see that you can make full missions in the matter of, well what I consider for how much stuff the editor includes, a short time. It is tedious for new players who want to create a simple mission have to spend a long time with it to get it working perfectly. Although if you're someone who likes being invincible in the middle of a huge battle with tanks, jets, helicopters, boats and infantry, you're also in for a treat.
Vehicles: The vast amount of vehicles in the game is incredible. Controlling the helicopters particularly takes a while to get used to. They don't jolt up into the air when you start the engine, you must wait for a short period of time to get it up. You may fly with the mouse or the keyboard, and surprisingly with enough practice are really easy to control the helicopter with. However AI's seem to have trouble controlling these unusual flying machines and tend to fly too low and crash into power lines or trees in the map. AI's tend to have trouble the more of them there are as it's calculating each of their movements and actions, meaning they might take a second to register that they can fire at an enemy, overall they're fun to play with but where the game really shines is....
Multi-player: Playing online with friends is a blast. The custom made mission 'Domination' is featured along a list of public servers and is versus AI, that are pretty hard unless you're storming the place with 40+ players varying between infantry, air, land and sometimes sea. There are 'City Life' servers where you can play as a civilian, or the police and sometimes other characters. You can also host your own mission that you created in the editor to play with friends privately or publicly!
Overall: The game is true to what a MilSim is, and so is its modding community for example the mod Advanced Combat Environment (ACE) sets to make the game even more realistic and succeeds to do so, as well as making the AI cope with the Military Life. It comes with its faults like AI and clunkyness but it's a solid title and keeps hardcore ArmA fans happy.
That concludes my first article :) I hope you liked it. And I hope it convinced you to buy this game :)