[@Zeroth]

Good questions all. I'll make a list as I answer them just to keep track and make sure I cover them all.

1: Does this take place during the same time as the games, or during any of the movies?

Truth be told I wasn't completely sure when to set the game in the timeline... but my thought process was a bit before the start of Shadow of Mordor kicks off. The black gate is still in the hands of the Gondorian Rangers and occasionally a task force of rangers and solders might get sent into Mordor proper to deal threats they've detected (Ie, an orcish warchief is getting a bit to big and powerful and they want to deal with it sooner rather then later) to add another danger players have to be aware of in an already dangerous land.

2: Will the players be expected to fight Talion himself or some other prominent characters?

The answer here is... maybe. Some characters like Hirgon of the outcasts and Lithariel of the Tribesmen of Nurn are present in Mordor already and are doing their own things, leading their own factions and actively trying to hinder the schemes and plans of the orcs (and Sauron as well to a lesser extent). Mordor is a big place so unless you're actively looking for them, they're actively looking for you or one of you is just plain and simply unlucky you're not likely just to run into them. That said, it can happen... and if players dedicate themselves to trying to deal with either of these factions, they'll logically try to deal with you in return to rid themselves of a thorn in their side. 

As for Talion... from the start of the game he's just a mortal ranger captain. He might be apart of a Gondorian task force heading into Mordor to deal with a threat to the Black Gate, but they're kind of short staffed so that will only happen if they seriously have to. Depending on how the game goes, I -might- kick off the fall of the Black Gate, removing the risk of ranger task forces at the cost of a threat that is in many ways much, much worse. Granted Talion is more of a threat to captains and higher as the Gravewalker since they're the ones he is actually after instead of the rank and file solders, but if you're both moving around Mordor the wrong place at the wrong time can happen... you can even try your hand at actively hunting him down for the glory, but that path to power and prestige comes with its own risks and trials. 

3: Is extensive knowledge of these characters, Tolkien lore, or the specific games required, since LotR related stuff tends to lean so heavily on that?

Not really. You're playing as Uruks. Sure they're not stupid by any means (well... most of them) but the very nature of orcish society does mean that your average uruk doesn't really have an in depth knowledge of history. They are taught from a very young age that elves are sneaky, back stabbing pricks who want you all dead, humans are generally untrustworthy because they hate orcish kind but the ones to the west cannot be reasoned with at all and must die... Dwarves are generally an enemy as well, but hatred for them is more a personal matter while hating the elves is almost genetic.

Sauron is the Dark Lord and while he is a complete and utter monstrous asshole who doesn't give the slightest shit about uruks or anyone under his command, he is still ridiculously powerful, has spies and agents everywhere alongside fanatics who worship him as a god and despite his detain for uruk kind he is one of the few leaders in Middle Earth who doesn't want to just purge all Uruks for the principle of the thing. You don't have to like him, but the only real alternative that uruk's know of to being under Sauron's rule is to strike out on your own... and if you do that you need to have a decently sized group of orcs ready to follow you out of Mordor to make a proper warband because everyone outside of Mordor wants you dead and staying [i]in[/i] Mordor after going awol is a hazardous state of being.

4: Is there an end-goal for the RP, a particular plot thread (such as a quest for Sauron) that would solidify the RP as an "evil campaign," or is it just a "see how long you last" kind of thing?

It's more of a see how long you last kind of deal... but depending on how things go we might develop an end goal. We'll see.

5: And are the characters limited in their strengths, weaknesses, other qualities, etc to the corresponding abilities and descriptions from the games? For instance, does a strength have to be something like "Fast Runner" or "Immune to Ranged," or is it more free form? Basically, are players picking from the game's wiki for their skills and development, or can we create freely with more customization?

No. You can freely customize abilities and developments, but keep in mind that I will impose weaknesses that make sense when the situation arises. For example if you get mauled by a Caragor and survive, depending on how some dice roll behind the scenes your Uruk might develop a phobia for the things. As for strengths... When a strength is earned, I'll have a brief chat with the player in question so that what they develop is related to the situation and makes sense for the circumstances. Slaying half a dozen caragors by yourself isn't going to make you arrow proof after all.