The setting of this show is pretty standard high fantasy, but leaves the door open for a great show - dragons, magic weapons, political intrigue: its all there. There are other things the show does right; the artstyle is crisp and very colorful and the few action scenes we do get are pretty well animated.
However, the most important part of any show is its writing, and thats where Lord Marksman falls flat on its face.
As mentioned, the setting is pretty cliche, but I have no problems with that. The big issue is the characters and the plot.
Every character in the show is incredibly flat, with the most shallow and simple of motivations. There is no real character development, no complex relationships. Every conflict is entirely surface-level. Even the mc lacks any depth beyond "hey he's really chill and shoots arrows real good". The show fails to make you care about any character beyond their outward aesthetics.
On top of that, there are countless elements of the story just being thrown around haphazardly with no connection. New characters and conflicts just kind of drop in randomly without any setup and are resolved just as quickly. McGuffins just appear out of nowhere and are either never explained at all, or vaguely mentioned once and then entirely forgotten. The closest thing we have to introducing an internal character arc is dropped on us in episode 2, basically never discussed again until the climax, and then once again is ignored entirely immediately after it comes up.
Overall, the shortcomings arent enough to make the show unwatchable - just boring. If you want an interesting fantasy story, there are countless shows far more gripping than this one. If you just want to relax on an afternoon and throw on a short show in the background with just enough bright colors and action to keep your attention while you work on other things, this is the show for you.