While watching my brother play through Grandia over the last few weeks, one thing I notice is that, in certain parts of the game, there simply isn't a lot of variety to the enemies. Many field areas and dungeons in the game average have an average of four or so enemy types, a fairly reasonable number, if perhaps a bit small, but some places are far worse than that.
The places in the game with the worst enemy variety are almost always military bases full of soldiers. It seems to be a rule in that game that every dungeon or major scene that has soldiers as enemies will have exactly one kind of soldier for you to fight, that will always show up in groups of three. They don't even show up in multiples of three, even though up to nine enemies can be present in a single battle, and instead just stick to groups of three. Other games that feature battles against soldiers tend to mix up the kinds of soldier that you fight, mix in other kinds of creature with the soldiers, and change up the numbers, but that doesn't happen at all in Grandia. You don't even get to fight the tanks that are seen everywhere in these dungeons. Even worse, every solider in the game uses a recolor of the same soldier sprite, and the soldiers all tend to fight using similar attacks and relative stats, so every solider-based dungeon involves battles just like the previous soldier-based dungeon. It is an incredibly boring lack of variety.
Soldier dungeons are not the only places with that problem, as well. One other place in the game, the Twin Towers dungeon, has only two kinds of enemies, and one kind is found in a single room that is visited briefly by a single character. The rest of the dungeon is filled entirely with weird medusa creatures and nothing else. This is all the more remarkable because this dungeon is technically occupied by the same soldiers you fight elsewhere in the game, but you can't break up the monotony and fight them there.
A somewhat less extreme, but still relevant example is the Typhoon Tower, an important dungeon in the middle section of the game. This tower is broken up into three sections: the path to the tower, the area around the entrance to the tower, and Typhoon Tower itself. The path to the tower is filled with nothing but a single type of monstrous plant enemy, and is thus about as boring as a soldier dungeon. The area around the tower is actually halfway decent, combining the plant enemies with new "Klepp Soldiers" (a type of bird-man monster) and Lizard Riders (Klepps that ride lizards). The tower itself is filled with six types of enemies, but these are broken up into three types of Klepp soldiers and three types of lizard riders. This would not necessarily be bad, but each kind of Klepp solider comes in the same numbers as the other kinds of Klepp soldiers, tends to have similar stats as other Klepp soldiers, and uses the same attacks as other Klepp soldiers. They are technically different, but only in the most minor ways. The three kinds of Lizard Rider are equivalently similar to each other. Thus, they may be technically different, but fighting an Elite Klepp doesn't provide much in the way of a new experience compared to fighting a basic Klepp Soldier. Thus, even though there is quite a bit of variety of enemy type in the dungeon, it still ends up feeling very monotonous and dull. The first stretch involves fight a lot of plants, and the latter stretch involves fighting countless Klepps that all fight alike, so other than the initial introduction of the Klepps there really is a lot of repetition and little variety.
The truly depressing part of all of this is that some other parts of the game have quite a bit more variety. For example, despite its small size the Castle of Dreams has five enemy types, all of which are completely different from each other and four of which were never seen before that dungeon. They range from high-HP, low-defense zombies that are weak to fire and use status attacks to low-HP phantom mages that are highly resistant to attack and use powerful attack magic, with everything in-between being equally distinct. What is more, these enemies show up in varying numbers and practically each room has its own combination of enemy types, so there is a fair amount of unpredictability and diversity. Yet, the Castle of Dreams is a small optional area, while the monotonous zones are large and important to the story.
I will admit that Grandia makes such repetitive combat more interesting than some other games, because the player needs to constantly build up different stats and has a fairly wide variety of ways of doing that which you may need to cycle through, but it is easy to get sick of seeing a particular enemy group when you have done nothing but fight that one kind of enemy for two hours of gameplay. Even the best combat system gets dull if you don't get to fight new things once and a while.