I heard the same before playing but once I started I didn't think it was very complicated at all.
First off before you actually get into real battles you're able to go to the Arena and go through an optional multi-step tutorial which explains everything. Not everything might register at first but that's OK. I think people say it has a high learning curve because there's several aspects to the combat (most of which you'll get once you get into the game), and because the combat is pretty different from anything else out there, but it's not complicated at all.
Pretty much all battles boil down to you doing scratch damage with machineguns then finishing off an enemy with direct damage using handguns or grenades (you can't finish off an enemy with scratch damage).
You've probably heard of Tri-Attacks coming up often when people talk about this game...the Tri-Attack is almost useless. It might be more useful on higher difficulties, I don't know, but I find it a lot more efficient to use a Hero Action (the action where you run fast and do flips and shit) with my machine gun user, charge up my gun as many times as needed to either break an enemy's shell before I can do more damage to it or if it doesn't have a shell, as many times as it takes to take off all or nearly all of the enemy's HP with scratch damage (you'll estimate all this easily as you fight enemies), then just finish the enemy off with a handgun/grenade. Or if I don't finish an enemy off, I can at least take off some body parts that defend the enemy's main body which allows you to deal damage to its main body (at that point is when you'll be dealing most of your damage).
Every battle has more or less the same tactic, and I heard of people saying it gets repetitive because of that, but I disagree. Many enemies have different types of resistances (I mean in terms of defending body parts and total HP, not elemental resistance) and combined with the different battlefields and enemy placements makes every battle unique. Thus I never feel like battles become a drag.
Some other tips:
-Customize your guns. Go to a tinkerer, find some parts that have some good numbers besides them (lol) and equip them. Upgrading your machinegun is the most necessary as that's the main damage dealer, handguns and such are there just to finish off an enemy really (handguns can also break HP gauges but you don't need to rely on that much), but customize all of them. You don't have to think too much about what to put, just put on something that seems good. Oh and you can move the gun on the grid around with a certain button, I just found this out today.
-Switch weapons between characters often. This game doesn't have a traditional form of leveling. Your levels are determined by the level of your machineguns, handguns, and grenades. So basically if Vashyron is lvl 10 in machinegun, lvl 8 in handgun, and level 5 in grenade, his total level is 23. By leveling up you can increase your HP and weight which is helpful. So switch weapons between characters all the time.
-You can dual wield machineguns and handguns. You can fire twice as many bullets and I think deal double damage as well. Oh and this helps you gain EXP in whatever you're using faster too. You can get a second machinegun in the Dakota Vein which is an optional dungeon. Dual wield that shit with your first machinegun ASAP. Considering machineguns do all the damage, they just can't finish an enemy off, you can imagine the benefits. However you need a certain weight to dual wield, but it's not that high. Which is why switching weapons is important to level up fast and gain more weight. Oh and to get this machinegun you need to kill two lvl 50 enemies at the final stage of the dungeon which are tough...but can still be easily beaten. Just terrorize them with
by equipping your machinegun user with the magazine case. They go down fast.
-On chapter 6 there's a fast money trick you can abuse. Look that up.
