Sorry Craig, I dont want it spoiled so didn't read any of your post haha! But I'm thinking of picking up Uncharted 4 soon, would you say I'd have to play the other 3 games to fully experience it? If so, might have to play the trilogy collection as well
Haha, it's all good, man. Apologies for the potential spoilers (which is why I threw the tag there to begin with).
But to answer your question... I would certainly recommend playing all of the Uncharted games, before playing Uncharted 4 and then ultimately, The Lost Legacy. If you can, pick yourself up a copy of the Uncharted remastered trilogy and play it back to back, go through one, two, three and eventually four. I think that way, you'll really enjoy the overall story as well as the characters.
I think COMaestro's hit the nail on the head, pretty much. Uncharted: Drake's Fortune is probably the roughest game in terms of game play and graphics (to be fair, it did come out in 2007). For its time, it was graphically insane, but you'll certainly see its age if you play it now. It's vital to play this one though, as COMaestro said, it introduces to us the primary three characters of the Uncharted franchise.
Uncharted 2: Among Thieves is a lot more polished, introduces to us new characters (such as Chloe Frazer, who is the playable protagonist of the just released Lost Legacy) and new game play elements. This is probably the best one of the original trilogy.
Uncharted 3: Drake's Deception is in my opinion, a good one too. This game continues Nathan Drake's story and even dives into his past, establishing his relationship with Victor "Sully" Sullivan. Uncharted 3 isn't as good as 2, but it's worth the play.
Uncharted 4: A Thief's End is probably the biggest Uncharted game released. Most Uncharted games... you can knock out in five to eight hours, depending on how good you are, but A Thief's End has a lot more content and larger environments, so it'll probably take twelve hours or so?
I do recommend playing them all and if possible, playing back to back.