In EO4 (and the demo of EO Untold), everything's basically in first person, which kind of disorients you are first. The key feature is cartography (map-making). As you explore dungeons, you need to create your map and note where things are so that you don't get lost. In terms of the battle system, it's all turn based. However, you're limited to whatever skills you teach your characters (you get a set amount of points to spend on abilities, which you have to budget since you only get three points per character to start and only one every time a character gains a level). There are different types of skills that have different effects: Dungeon skills allow you do things in the dungeons you explore, battle skills help enhance your characters combat abilities, and rune skills are basically this game's version of spells.
On top of that, the game's enemies can't be taken down with straightout attacks. Generally, you'll find yourself trying to cripple them with status afflictions and weak binding attacks somehow before you can actually kill them.
To add to that difficulty, there are powerful set enemies called FOEs (I forgot what that stood for though). FOEs are the enemies that can kill you quickly no matter how strong your characters are. Eventually, you will get to the point where you can take down weaker FOEs without much effort, but other versions of the same monsters tend to stay stronger than you as you progress through the game.
EO4 is pretty addicting, but it gets a little frustrating when you find yourself constantly running back to the main town in the game just to heal your party. There are characters like Medics that can heal your group in the field, but they become a little ineffective when your entire party's Tactical/Technical Points (EO's equivalent of MP or PP) starts to dwindle from constant skill/spell usage. It's truly a game of survival.