Riviera was a great idea on paper, but in practice it divided the game into two completely separate play styles. You either knew what you were doing and constantly walked over the game, or you didn't and got your ass constantly handed to you.
The game wasn't about the combat though imo. It is a pretty easy game unless you totally fail to understand the basic game system (though I haven't tried a zero grinding run). It's not complicated. It's more about the characters, relationship system, and having lots of choices to make at various triggers throughout the game.
It kinda leads me to my beef with the Grandia series on the whole. None of the games have a decent cast. Its basically the main hero, the chick who turns out to be a walking plot macguffin magical girl, the buddy, the twerp, the older guy/sudo mentor, the android chick found in some ruins, and maybe another chick who's both the least dislikable and only shows up for a dungeon or two then gets ditched/bails. Also the settings file themselves right into the same bad writing category as FFVIII's setting (i.e. they disintegrate into a goofy ball of cobbled together analogues, metaphors, cliches, and elemental based gimmick dungeons, the very moment Mr. Scrutiny violates his restraining order to stay at least 50ft away from the writing).
Millenia and Sue are the best characters. Millenia is barely ever in your party and Sue leaves less than halfway through G1. Overall plot is weak in all the grandia games but I do like those characters. Didn't like any of the G3 characters.
Also, Ryudo was a fun main character until his personality totally changed :P