That guide is really good, short and to the point too and pretty much sums it ALL up. The only thing that makes an ND different from a GD is the whole DoTA lets-play-gate-defense game, and the fact that every mob, when tagged, spawns two 'fake' reinforcement mobs.
On the subject of reinforcement fakes. A lot of ppl seem to have trouble with understanding the latter though; that when you tag a mob, regardless of it being 'real' or 'fake', it will ALWAYS spawn two reinforcements that lock on and agro you. It gets really annoying when in an extremely small crowded room as when the reinforcement mobs spawn, it's possible for them to agro someone NEAR you that's out of battle... This causes them to spawn TWO MORE EACH and... yeah. It's possible to wind up with a higher mob counter than what you started with. With Ghost Ship, the way to tell a real from a fake is if you inspect the mob (patrol lic needed), real mobs have Mimics, reinforcement fakes don't.
Otherwise though, that's the ONLY real difference between ND and GD.