This is more storyline then really talking about the game mechanics wise. But is it me or is Melvin kinda an ass? I mean he's crazy what self respecting DM thinks the whole point is to be OP and be a complete asshole and kill everyone by doing 300 damage to a 20hp char? He needs therepy....
Melvin is fashioned to represent the Dungeon Master who thinks the game is about himself and his control over the story and the players. In general, those DMs end up being real jerks and make the game a bad experience. If you play D&D (or any RPG for that matter) you eventually run into one. So, yes, he is meant to be that way. Hopefully you're enjoying Gary's optimism and his crush on the pizza girl in spite of Melvin.
See Melvin is the classic case of the big dorky fish in a little dorky pond syndrome. Typically a person like Melvin feels powerless and more or less isolated in the wider world. But in the microcosm that is the fictional Card Hunter world he is both powerful and semi-important. So instead of acting reasonable or considerate, he instead lashes out in a manner that he subconciously feels is how the world works, specifically those with power abuse those without and those with knowledge condencend to those without. Basically he is just a bully due to his perception (or the reality) of him being bullied in his life otherwise. This is opposed to Gary, who probably having some similar experiences to Melvin, tries to basically follow the Golden Rule. Melvin thinks he is following the Golden Rule, but he has mistakenly learned it as he who has the gold makes the rules. In other news if you find the single player difficult and it certainly can be especially at certain adventures where the diffiuclty jumps Additionally if you have never played a strategic game before learning critical strategies such as when to advance, vs. letting the opponnent come to you, how to use a team together (starting first with making sure you kill opponents one at a time instead of injuring a bunch but not knocking anyone out). The twist with this game is that the best build generally doesn't work with every map. Sometimes you need armor workarounds (armor destruction or penetrating attacks) sometimes you need to avoid certain damage types (e.g. crushing) and sometimes you need to just have a little extra movement. Good luck, have fun and since you already found the forums you can get a LOT of information if you get stuck on a mission.