I seriously think the SP would've been much better if they simply added in more enemies to fight. I was really happy with the Ork fights in the campaign for the most part - although some parts could've used a lot more variations and numbers of greenskins.
When it came to the Chaos chapters, I thought there was a severe lack of Heretic Guardsmen to fight in most parts, and there could've been way more variety to the Chaos Marines - most of the time it felt like it was just some heretics, bloodletters, and plasma havocs. There should've been more havocs with heavy bolters, lascannons and autocannons. As for heretics, I think we should've got to fight large waves of heretics, and have them entrenched in heavy cover with heavy weapon teams. I was particularly disappointed with the Chaos Marine tacticals; I think there should've been more variety of them using different combos of chain axes w/ pistols, chainswords w/ bolters, meltaguns etc - there jsut seemed to be a severe lack of Chaos Marine melee fights, except for the Maulers which were pretty fun, but rare to encounter.
The game runs very smooth on the Ps3, so I wish they could've added way more enemies on screen at least, or at east more waves in certain parts - the game felt way to barren in many parts unfortunately.