The final Nailgun upgrade really improves the viability of the weapon. Besides the Rocket Launcher, no other weapon get quite the same level of improvement. The modification adds a scope to the Nailgun, enabling you to "lock-on" to an enemy so that your nails home in and deliver their considerable collective damage. Ironically — considering the weapon's Gatling Good design — the homing nails make the weapon into a effective sniping tool.
Receiving the upgrade for the Rocket Launcher really takes the weapon to a whole new level. What makes it notable is unlike most of the weapon upgrades (Nailgun aside), the modification drastically improves the weapon. Now you can fire off three rockets in quick succession and at any time, can use Secondary Fire to activate the laser-guide to help guide the missiles to their target. The rapid-fire feature is very helpful against Tactical Strogg ambushes as the Splash Damage of a rocket salvo will make quick work of them.
Nexus Core is the final regular stage that the game has been building up to and it delivers. You must make it through a gauntlet of heavy resistance, with the Strogg throwing plenty of Tacticals at you but you've likely got plenty of ammo for all your weapons and can mow through them with your heavy weapons. A Boss Rush awaits you in an arena right before the final stretch with the remaining Nexus garison. You'll be at high risk of dying but the challenge feels just right for the pen-ultimate level.
The Nexus and your last fight against the Makron. They're very fun to fight and also fair with sufficient cover in the arena to give you a fighting chance. The musical stinger the Makron enters to helps get you excited. You then get to destroy the Nexus core as it constantly spawns hordes of all kinds of Stroggos, from simple soldiers to Heavy Hovertanks. Not to mention that the pose that Kane strikes during the ending, upon destroying the Nexus, looks utterly badass.
