I think, if you're enjoying doing it, and will enjoy having done it, then do it. Don't worry about the people that don't like it, unless you're planning to force them to play it. (Don't do that.) But if you and others will enjoy it, those are the folks that matter.
I was going to say that while this is very true, some constructive criticism goes a long way towards improving, but having now gone through the thread in question, I can now just say "Very much this".
I know next to nothing about Marathon (but might check it out eventually, our of curiosity if nothing else), but the screenshots you shared look pretty good. Just keep in mind that this is the Internet, and there's no shortage of folks who'll be willing to diss someone's work. Either they genuinely didn't enjoy it (not everything's for everyone. Let them be. Listen to their criticisms if there's any value to them. Then focus on the people who do
enjoy it), or they're just expressing some general negativity, in which case you can probably safely discard their opinion.
And as SBN said : if you enjoyed making it, that's the main thing. The fact that people would contribute out of the blue to make it better shows that there are people who have enjoyed your work. Always remember that