Found a strange glitch in the last area with the Boss Troll, I'd already beaten the one you can find in The Den and got the ending. Then I continued to play without restarting and went to the last area and found that 2nd Boss Troll and killed it, but the objective to find the troll never triggered (the one to kills the troll did trigger however).
I was able to get around this bug though, by leaving the level (by pressing escape and leaving), and then reentering the level. Once in the level again the objectives to find and kill the boss troll were no longer there, and I could simply find the 3 objectives (during the initial scouting mission for the area), and then leave the area.
I had played through from the start on Hard mode, wasn't that hard really, though I'd experience with the last 3 games. Got to Hard+ mode but decided not to continue. I unlocked all of the equipment and upgraded it to max.
It's nice once you get the bases so that they can no longer be attacked (this can be achieved without upgrading the base defense weapons/militia/factory to max). I had about 26 or so spots for recruits around mid-game, and filled them with nothing but the engineers and civilians that generate 150 & 100 gold.
With I believe 4 bases all unable to be attacked, without having fully upgraded them except for the 1st base at the time I believe (which is easier than the others), I was able to click the Zzz button to sleep through hundreds up days to generate 2000-3000+ Gold per day. Getting the items and upgrades was easy at that point, as was upgrading the bases. Once I figured out a few good areas to check for people to recruit on strolls, the game became pretty streamlined.
I didn't bother comparing if Captains were better than Rangers regarding their respective weapons, but I decided to bring along 6 Rangers using the Commander skill, and they were more than sufficient to help get through all of the late game, using mostly the Minigun, sometimes the Rocket Launcher for groups of fragile enemies, the Poison modification of the Pistol to have enemies (specifically lower ranking Trolls) help you, some Grenades for groups of weaker monsters, and bunch of Mines laid usually when defending an objective. You also get to use the Mines and Grenades for base defense it seems.
There were some nice additions and subtle changes in this iteration if I recall the earlier games correctly. There seemed to still be a bug I recall encountering from earlier games where, when enough gunfire is focused on 1 unit, it appears as though block hitboxes become visible, or something of the sort. It kind of looks like shadows. I think it only happened (rarely) once I'd my 6 Rangers helping me focus fire.
The thing I dread most about these games is being forced into defending the bases, which is why I attempt to make them unable to be attacked as soon as I can. I don't want to spoil how one does that, I'll leave that to the other players.