Grid, as a character, can be a bit annoying to start with. He whines about how unfair the world is and refuses to take personal responsibility for his actions, but as the story progresses he begins to change his outlook on the world. I've gone back and reread the story from the beginning a few times' and in doing so, grown to appreciate his character progression.
Grid doesn't completely flip his personality from the beginning, but the difference is noticeable. He's been humbled by his experiences, but still has enough of an ego not to allow himself to be stepped upon. He has enough confidence to know what he excels at and to work on his weaknesses. He's able to recognize the contributions of others and reward them accordingly. When he does act like a scumbag, he's at least self aware enough to feel bad and make amends. I don't see him going from one extreme to the other, but rather becoming a better adjusted individual who still has some quirks.
His out of game life at the start isn't pointlessly tragic as commonly happens in Korean novels. Things aren't looking grim for the sake of it. A lot of the things wrong in his life are the result of his own actions. As someone noted earlier, Grid is impulsive, which leads him to do things that weren't well thought out. Grid's in debt because he spent a ton of money on an expensive gaming capsule without the means to pay for it. His parents are alive and they scold him because they see him wasting his life away as most Asian parents would. He seemingly doesn't have any future prospects because he dropped out of university and he doesn't have a steady source of income because he's saddled with debt due to his gaming addiction. His poor social life is linked to the fact that he's got no job/money and all he does is play video games all day.
I think a major difference between OG and LMS is how author's treat "NPCs" in the VRMMO. From what I remember, there aren't any significant NPC characters that stick around for a while in LMS (aside from sculptures/pets). OG takes the approach that the NPCs are equal to players in their importance. They have their own motivations/desires and play major roles in Grid's story beyond just being quest givers. That isn't to say that Grid only parties with NPCs, but that they're more than just window dressing.
Plot progression seems smoother than LMS as well. There were many times in LMS that I skimmed over passages or even skipped them because progression ground to a halt and got boring. Obviously the scale between the two novels is significantly different since each one of LMS's chapters is drastically longer in comparison, but I've reread OG 3+ times at this point and I've completely dropped LMS. I enjoy that OG resolves things in a timely manner and doesn't linger too long on them. Some plot points are set up arcs in advance and revisited at a good pace. I can't recall off the top of my head any arcs that overstayed their welcome to any significant degree.
On a side note, Grid's not as ugly as I was led to believe. I suppose it makes sense, but its kinda interesting as well.