So you're saying I should redo the bunkers? I did do them really half-assed. I think I'll would also need to increase the size of the beach's width if I want to achieve the feeling you're telling me to go for. I mostly added the sandbags because I wanted some kind of cover while people went from bunker to bunker. Also, what do you recommend exactly for the cliff faces? I find that the cliff was done well, even if it lacks some detailing.
What do you mean by "Try not to fall into the standard traps with D-Day DMs though"? By that I'm thinking that you're telling me to have my build well detailed+proportionally sized.
I recommend you keep on doing what you're doing with the cliff faces; I mean that, the beach section of D-Day is usually drawn out and is boring; the cliffs should then be focused on instead.
Increasing the width would not hurt, provided you break up the beach ( I suggest a cliff reaching out into the beach to separate it into sides or whatever)
Cover should be there, just some sandbags (the sandbags are well done, though, so just some) should be replaced with extensions of the bunkers: extra rooms, concrete walls, et cetera.
The standard D-Day traps are basically
1) prop spam. Usually, a flat and otherwise plain surface is laid down, and a bunch of crates, boat traps (which are iconic of D-day because of the low tide whatever) and sandbags are put everywhere. The props define the map instead of the terrain and buildings defining the map. Bad.
2) focus on a death run over the beach. May be more realistic but it's boring.
3) lack of objective. Usually combined with 2).
Functionality > detail, the problem with prop spam maps is that, while props are extremely detailed, they lack functionality. Terrain, cliffs, structures. Functional.
Proportions are also important; the areas that are more interesting (hint: not the beach) should be emphasized. Personally, I suggest that the defense is given a far back spawn, but setup time at the beginning so the first few minutes involves the beach (as the defense has had time to get into position), but the gameplay moves backwards towards the defense spawn area (as the original defenses die and cant be replaced quickly enough) to provide a change of pace that feels natural and is purposeful (siege points?).
Overall: standing on a beach wedged between a crate and a grey X is only interesting for a little bit. Let the offense progress into more interesting areas, while maintaining (respectfully) the iconic beach.