The second issue is the gigantic H-cup power titties, the man face, the absolutely terrible in general minis and the absolute lack of care GW gives them, the fact that they are intolerable fanatics of an extremely vague and ill-defined religion (we have no idea how the Imperial Creed feels about, basically, ANYYTHING applicable to modern morality, so unless you're fighting aliumz or chaos you have no idea how your characters would feel about it, but you know they'd have an EXTREEEEEEEEEEEEM opinion).
The -general concept- of them I like, they are amongst the most Imperial-flavored of Imperialtown. The space marines are the most visibly iconic 40k faction and they are not part of any Imperial law or command structure (except the Highlords) and they do adhere to the Imperial Creed. And they're so few they're almost nonexistent... so space marines are kind of terribly non-representative of the Imperium.