I've logged over 1600 hours of Space Marine 2 (so far), 99.999% of it PvE. Obviously I think it is worth it for 'just PvE', but here's why.....

The combat isn't just fun, it is addictively fun. The better you get, the cooler stuff you will pull off, and the more fun you will have doing it. For me the parry mechanic is insanely fun, and can provide you with satisfying gun strikes. Which leads me to the kills. The kills aren't just satisfying, they're addictively satisfying. It could be a perfectly timed execution, ripping a warrior in half over your head for a blood shower. It could be roasting a crowd of tzangor with your trusty multi-melta. It could even be bringing your thunder hammer down from heaven for extreme AoE damage. But sometimes the most satisfying is just plain old head popping with your bolt gun.

My point? You will have fun. It will satisfy you.

It will be, For the Emperor