Nuno69 got a lot further in the game than I did, but I had a character from each class.
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My soldier and summoner were my highest classes. Soldier was 17 I think, and summoner was 20 or higher.
Summoner is cool. You could summon creatures to fight with you, starting with a bubble. The next thing I unlocked was a polar bear with frost breath that could attack from a distance. I think you could have two creatures at the same time. The creatures would level up as well, though they would reset to level 1 if they got defeated. Summoner also has a skill blackfire, which fires magic in all directions accept behind you and can help your summons hit enemies. I didn't have any trouble in higher level areas because summoner doesn't need equipment like soldier does.
I saw Nuno play as a soldier and he had a horse, some really nice armor and a good weapon. So he was able to fight in most areas on the game. I think he got to level 24.
I quit before the translation broke because after level 15, it starts to become very hard to earn equipment and skills. I couldn't find my level 25 skill for summoner, so I wasn't sure how to advance. I think you might have to defeat the king zombie and get him to drop skill books, but he is very rare in the mines and can be hard to defeat. My polar bear could do it, but he didn't drop anything when I beat him.