Keys to developing a great mission for ARMA/ALiVE IMO...
1. Balance: As Heroes mentioned, you won't want to be so overpowering that taking out the enemy is no challenge. Loading up on 2-3 Apache attack helicopters in Insurgency Missions against Taliban with limited Anti Air defenses can ruin the fun in a hurry as those choppers destroy everything around them.
As far as Troop levels, I typically control the levels of Opfor and Blufor by keeping Blufor in Military installations (FOBs, Airfields, etc.) and only going to highest priority Cities with the Civ Placement module. That way, the smaller, more remote villages can become Taliban/Insurgent hotbeds.
That will allow your human controlled units to get plenty of action while on patrol and it will also allow the mission to go on for quite a while as BLUFOR doesn't just wipe out all OPFOR groups quickly.
I also deliberately don't sync the OPFOR Civ Placement Module to the BLUFOR AI Commander because..as an insurgency...there should be less solid intel on where actual "enemy lines" are. They could be everywhere. BLUFOR will still go into these areas because they have their own CIv Placement module as mentioned before..but again...their own module in my games is set for them to occupy only the major cities and not the remote ones.
2. Ambience: If I'm in Africa, I want to feel like I'm in Africa. If I'm in Afghanistan, I want to feel like I'm in Afghanistan. Adding little things like news broadcasts about the region, regional music, etc. can go a loooooong way to really taking your mission to the next level enjoyment wise.
3. Flexibility: I try to make my missions flexible enough to be enjoyed by 20 players or 1-4 players. ALiVE is PERFECT for this. With the Command Tablet, etc. you can run very large scale operations with a skeleton crew of human controlled units. In fact, the updates to ALiVE's Command Tablet structure came directly out of Spyder and I's small group missions. We were wanting easier ways to run missions with multiple squads, Combat Support, etc. Spyder, wrote the script...tweaked it..combined it with what ALiVE already had..and now we have THE single best framework of any ARMA 3 Mod available today for running full map battles and operations.
Spyder Addons are another mod that was birthed from our small group missions. Vehicle spawners to give you instant access to any vehicle type you need without having to place them before hand. Troop spawners to augment your force for larger scale assaults. Ambience modules to provide immersive Civ Traffic, vehicles, even surprise insurgent attacks.
Anyway...those are my 3 areas I always focus on. Balance, Ambience, and Flexibility. As I mentioned...what you are looking for is, in my opinion, precisely what makes the current state of ALiVE so great.
