BTW, if our resident Naughty Dogger jlanier is still around, I have a free suggestion for the plot of UC3... this time have Drake and company follow clues left by Ponce de Leon in a quest to find the Fountain of Youth.
Maybe Drake's mom also had the exploration bug in her, and wants to find Drake's dad who disappeared looking for the FoY. She convinces Drake to help her out, and he wants to help her stay safe though he doubts the FoY is real. Throughout the adventure, he does the muscle work, she does the mental work.
Their mother/son quirky back-and-forths would provide the bulk of the character development, with a few added side characters as well. Scully argues with himself as to whether to make a move on her, but in his humorous grumpy way, he often decides against it since she's fat and wrinkly. The two insult each other (for laughs) for most of the game.
Maybe one action scene is a flashback as they talk of mom teaching a six year old Drake how to fight bullies (dad was thought dead by Drake and mysteriously is absent). You control Drake in this difficult encounter. Another interactive flashback is a daring mini-adventure featuring Drake's mom as a young woman, where she also meets Drake's dad who was her friendly adversary at that time.
The present quest for the FoY would have new enemies of course. For instance, in a side trek into Africa they can fight off bands of pygmies who shoot poisonous blow darts at you, and include encounters against enraged, charging elephants, tigers, gorillas, etc. where you must use tranquilizers to put them down. Standard thugs with guns looking for the FoY would be frequent as well. Maybe take Drake back to the ocean and have a vehicle battle between high speed boats and pirate ships.
The final area can be guarded by a three, acrobatic Amazonian bosses who are hard to target due to their gymnastic skills, and can heal themselves by taking a dip in the fountain. Perhaps Drake is beat down, and only after his mom drinks from the fountain does she become young enough to take on the whole tribe with crazy acrobatic moves of her own (you distract the Amazons somehow so she can gain the upperhand). Eventually she saves the day. Scully is of course overly excited to see her in her new condition when the battle ends; of course she rebuffs his advances.
Having earned their respect by defeating them, the Amazons ask that the young mom stay as their sister. They show that they've captured Drake's dad, who found the fountain and is now young himself. The curse of the fountain is that for the price of eternal youth, those who drink of it must stay near its area of influence for eternity or they will die.
After an awkward reunion, Drake's parents say that it wouldn't be natural to be stuck in one spot forever, being the wandering spirits that they've always been. Together at last, they hug and kiss, and give wise words of encouragement to their son. They then choose to bravely head out into the sunset where a crying Drake, held back by Scully, knows that they will meet their fate after disappearing over the horizon.