I think the Imperium of Man faction could do a little, well, a lot of work.
As a huuuuuge 40K nut, some things with the faction were a little annoying.
Chainswords being 2 handed, laspistols being named wrong, and being a rifle not a pistol. Only 3 classes and 2 of them are almost dissimilar from each other and 1 class nobody can ever use. Seriously, I've played for a good 20 hours or so with the IoM and I only saw an admin using power armour, and even then the thing has no backpack.
What I think should be done;
Give the marine class scout armour. A little bit better than guadsmen flack armour but still affordable.
Give the guard a 4th class, the Commissar. Give the black commissar armour, a bolt pistol and a power sword. This can be like the close-combat class seeing as guard get wrecked by almost any army that can swing a sword faster then the behemoth of the chainsword.
A 5th Class, considering every other faction has a good 6+ classes this is hardly unreasonable. Stormtroopers/Kasrkrin. Let them choose to buy Carapace armour, a heavier, more expensive armour, but has more defense, and the Hot-shot lasgun. A lasgun with a lot more damage, but a little less accurate, smaller mags (Around 15 not 30) and longer reloads.
Change the bloody 'pew pew' of the lasguns. In every bit of lore in every black library book or codex it is described as 'the snap of lasgun fire' or 'The crack of lasgun fire' never 'pew pew pew'. They should sound more like the world war rifles, not star wars blaster rifles.
Different chapters and more accessible power armour. As I said earlier, it's basically impossible to get power armour. Most I have ever seen legit is the helmet and boots. It would be nice to drop the price down, quite a considerable amount, even if it means nerfing the armour. Also would like to see different chapters, IE. Ultrasmurfs, Minotaurs, Salamanders, Space Wolves, Iron hands, Imperial Fists, etc.
Also just rename a few things. It's Laspistol, not lasgun pistol. A bolter/bolt gun's ammunition is not 'space bolt' It's a bolt or 'bolter ammunition'.
If this game out as a very *****y rant. Yeah, it basically was. I am a giant Warhammer nerd, I know far too much for my own good.