If you don't mind going into multiplayer games then Defiance looks pretty good.

You could try pocket snooker. You can play by yourself or you can even have a second player. It's very fun emotional experience.

You did say role playing but not which setting :)

ARMA I/II:

Completely open world, with the ability to freely explore whenever you choose (between quests of course).
In this case between missions. You can move freely on the map, but don't be disappointed if you just cannot run into an enemy base without being captured or killed.
Usually it is best to choose your terrain and approach wisely, before running off.

Plenty of customization (even if just mostly cosmetic)
Totally customizable, play current time against terrorists or zombies, WW2 (extra game based on this engine exists), Vietnam, you name it...

Plenty of items to discover and use
Any weapon or weapon mods, vehicles, planes, helicopters, tanks, ships, bicycles, motorcycles you can imagine.

Quests than can change based on your actions and words.
The main plot has probably 3-4 ways to finish, join the enemy for example. Within missions you have completely free hand.

Multiple possible builds/play styles.
You are a human and there is no character sheet. Your eye/hand coordination and tactic defines your skill-level, but you do get better weapons/equipment from dead enemies or find them and therefore increase your abilities.

Unique in either it's art style/art direction or world design
This is no jump around FPS shooter (there are such multiplayer maps, though), mostly it is tactical in nature. You also get to command groups and larger troops on foot or armored/airborne while actively participating in the fights.
Or play it as MMORPG: http://dayzmod.com/

Not too easy (no "press this button to win" type of games) and not too hard (no "you misused one skill point, therefore your build is now entirely useless" games)
You can make it as hard or realistic as you like or as easy as you like. There is a steep learning curve involved to play this game.
You get hit by something, you are injured and probably bleed. So you use a bandage to stop the bleeding. You cry out load because of pain and the NPC react to this, no sneaking any more. You should try to find or call for a medic!
You get shot badly, you roll over the ground and cry out load in pain. You die quickly without help, maybe one of your NPC team members will drag you to the side and provides first aid.
You get proper shot, you are dead and start from last save.
You tank or plane is destroyed and you made it out. You are probably injured and what remained of your crew? You could try to capture an enemy tank or plane or fight on as ground troop etc.

To sum it up, you either get sucked into this game or not. The community content is the best part of it. The mission replay-ability is very high, due to the randomness of the outcome and you can always adjust the difficulty level or the level of realism.

The regular old Mount & Blade is pretty fun, offering a variety of play styles that you can try out to challenge yourself if nothing else. Try being infantry, for instance. Try taking over a country entirely on your own, without the backing of another nation. Try.

Borderlands arguably fits the bill as well. Both games are fairly linear but there are sidequests and shit to distract you, plus DLC done right for the most part.

IIRC Sleeping Dogs started out life as the 3rd in the 'True Crime...' series, got dropped by the publisher, picked up by another one and was re-invented as a new IP for legal reasons

however I do NOT recommend the PC version of the first one - Streets of LA as the controls are horribly broken - its a game that demands you use a joypad without joypad support!
Even if you use something like XPadder you're still stuck with digital car controls that are twitchy as hell - its almost impossible to drive straight down the street, you're constantly correcting from too much left to too much right, zigzagging along!
The second one might be better, not sure!

Total Overdose is in the new weekend sale, pretty cheep, its on my self but I haven't tried it yet - can anyone recommend it?

Oh, I thought the list of games in the OP referred to the games you already played, so I suggested something else. Did you actually mean to ask which ones of the games on the list we would recommend?

I know not all completely match up with my requirements, I tried listing every game I own that fit my requirements and/or was likely to be recommended.

You know, I had finally finished the hospital level in Deadly Premonition not too long ago (with your help), then I had to get a new laptop. So if I want to play Deadly Premonition I need to start from the beginning...and I'm probably going to do so fairly soon. Speaking of The Cat Lady, I need to see if I can re-download Downfall, since I had bought it from Screen7, if not I'll just repurchase it here.

I don't know much about that series, are they at all similar to the Geneforge series?

I'm open to any setting/theme really, the ARMA games seem somewhat complicated, and I mean that in the best way possible. I'll definitely check them out.

Are there any huge differences between the original Mount & Blade and Mount & Blade: Warband, besides being able to form your own kingdom in Mount & Blade: Warband?

I've tried Borderlands 2 in the past, I really liked the art style but for whatever reason I didn't really enjoy the gameplay. Maybe because they start you off on something similar to an escort mission haha. I'm willing to give it another chance though.

The games I listed in the original post are games I already own, so I'm looking for suggestions of other games to get.

Thanks everyone for checking this thread out and recommending some games!

Any other suggestions? I bought Planet Explorers yesterday and I'm really enjoying it so far, it's like a combination of Outcast, Morrowind and Minecraft.

Hmm...how about Ultima VII? It has a lot of the things you asked for: Big world, lots of stuff to do, a book of many spells and more. GOG even sells it with all the dlc so theres more stuff to do. Sadly, I havent played so I can't give you more details. I've just seen videos about it and it does look like a great game.

- Risen 2?
- Elder Scrolls Online?
- World Of Warcraft?

Good recommendation, thanks!

I didn't really enjoy the first Risen so I'm not sure whether or not to take a chance on Risen 2, what are your thoughts on it, if any? As far as your other suggestions, I'm one of those odd gamers who doesn't play online games/games that feature a monthly fee haha. Thanks for the recommendations!

I've never played Risen 2 but it looks like a decent game. If you have money to throw away then it might be worth a try, considering it seems you have every other RPG known to man. :)

Fever_Discordia mentioned Total Overdose and I can vouch for it. It's not an RPG and maybe it's too "modern" and fast-paced for what you are looking for, but it meets pretty much all of the requirements you made; it's open world, not too easy and not too hard, it's offline single player only, has a very unique artistic direction and world setting, you have LOTS of stuff to find and collect, you're free to roam the world as you please -- between missions, that is --, looking at the people going about their lives, and you can customize the character (not cosmetically, though, unless you count weapons and an item that turns you into a fat sluggish luchador*).

You listed the Just Cause games, so I guess Total Overdose should be a no-brainer.


*- for a brief period of time only, during which you have to fight other luchadores in order to collect melee weapons.