I am mostly familiar with their Utawarerumono and Tears to Tiara.
They had mediocre tactical RPGs (but at least they're not clones of X-COM), mostly vanilla H-scenes that were often just randomly thrown in, and awesome stories.
Expect things to suddenly become epic, and/or to merge sci-fi and fantasy in the "slicing a giant robot with a katana" manner.
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Now my own question:
Do I need to be familiar with other "Dungeon Travellers" games or "To Heart" games to play this game? Will I be missing a lot?
Not sure if you need to play To Heart 2 first. Even To Heart 2 has new/separate set of characters/settings to To Heart 1.
As for if you need to play other "Dungeon Travelers" first, this one is the first game of the trilogy.
Dungeon Travelers 2 (2nd game) has new set of characters/settings and different MC as well to this game. so the story is stand-alone. However, To Heart 2 characters are all playable as DLC in Dungeon Travelers 2.
However, Dungeon Travelers 2-2 (3rd game) uses the same characters/settings/MC from Dungeon Travelers 2 but with some new faces. So playing Dungeon Travelers 2 is recomended to get acquaintanced with characters and locations.
if you're planning to play all three of them, I'd recommend start with this one as it's the least polished game compared to the later games such as less max inventory limit and no Spieler class until the second game. Kinda feel a bit inconvenient to go back to the older game if you already get used to features from the later one.
Just in case if you don't know, Spieler is the 5th class besides Fighter, Magic User, Scout and Maid.