This is a very impressive and detailed map (speaking as someone who's mapped various parts of these same islands at various scales over many years)!

Appreciate this is for game use rather than historical precision. However, the lines of both the Antonine and Hadrian Walls are a little off their actual ones - Hadrian's Wall follows along not far from the north bank of the Tyne in its later eastern stages, and ends at Wallsend (surprise!) on the north bank more or less opposite Jarrow on the south bank (at this scale), for instance. Not sure how important this may be for your purposes though 😊.

Seeing what else has been labelled, it may be worth thinking of adding some names for the more important old Roman roads, as some at least were still in use by the c.560s CE and later (some major roads still follow their lines today), and a few of the surviving names seem to have their origins in the Old English/Anglo-Saxon language.

So far as I can recall, there isn't a specifically runic font available for use in the Community Atlas list (which includes most of the PF-provided fonts and those from a standard Windows 10 installation), although that isn't fully up-to-date, as it doesn't include fonts provided by ProFantasy in the Annuals from the last few years.

Your best option would be to find a suitable font online, either free or paid-for, depending on exactly what you need the font for, install it, and then use an exploded version of that if you're wanting to submit the map for the Atlas. The fact you can't edit it after exploding it is a disadvantage, although that really depends if it's meant to provide functional labelling (which someone else might wish to amend if they have access to the FCW file), or simply for decoration (such as in a map border frame).

Structure markers - yes, some probably are too large. You might need to replace the hollow centre to the Town and City ones with a contrasting colour circle/diamond instead of being hollow, if reducing the sizes (looking at the way the smaller markers are on the map now).

The craters look nice, although the pale outer rim is a little too sharp and dominant at present. Crater rims tend to end up as a relatively gentle hummock-line very quickly, through a mix of natural slumping during to soon after formation, and weathering processes. Currently, the rims look a bit too wall-like.

They all seem perfectly fine to me, Sue. Natural terrain colours don't always match quite how you'd expect, and can change under variant lighting conditions anyway.

I can also see that "patchy" texture look working well for different kinds of swampy lands, with a suitable water texture showing through between the islands.

Late to the party, but lowland tundra is essentially cold, dry and treeless. In general, it's the name used for such treeless places where the ground is permafrozen a short way below the surface, so shallow lakes and bogs are common, when the topsoil's frost thaws in summer long enough for hardy, low-growing plants to survive. Alpine or mountain tundra is similar, but its treelessness is because of the poor, thin soils, and colder, higher altitude air, as well as general dryness. Lakes and bogs are less common, as the drainage is often better in the higher mountains. It's all downhill from there, after all 😉.

Red desert sands are fine by me too - handy for anyone wanting to recreate Martian landscapes, of course!