I think it's bound to be better thanks to addition by subtraction. Instead of DeRozan, Gay, and Mills soaking up heavy minutes, we have a stable of young athletic players to mix and match, and are deep enough to swap guys out regularly so they can defend with intensity and not lose their legs.
Murray, White, Vassell, and Poeltl are all plus defenders. Eubanks has come a long ways protecting the paint.
The largest concerns are probably McD and Forbes, obviously. Both rank in the bottom of the league in advanced defensive stats, and both figure to have a prominent role. Hopefully we don't see both on the court incredibly often so there will be enough help around them to hide them on that end.
The real wild card is Walker. He has all the tools to be a good defender, and yet he struggles constantly in that regard and is actually not ranked far from Forbes. Not sure if it's just a matter of misunderstanding or if he is simply not giving the effort consistently, but a lot will be riding on him this season to prove himself.
I think last night was a good example of how the team can not only create havoc on defense with lots of switching and hounding passing lanes, and then funnel that into scoring opportunities in transition. Obviously, that was against a hapless Rockets team, but that could be their best strategy for this season.