I like to hear that developers look at other games and take inspiration from it, as long as they still do their own unique thing in the end. Multiple stuff that came up, probably this will be TL;DR for most, but I feel like rambling.
The Witcher 2 in general:
I've been a huge fan of the Witcher 1 already and pretty sure the Witcher 2 is very good too - however, I owned it for a few months already and still find reasons not to play it because I couldn't get over the damn worst UI ever made, so I really can't comment much on it. But the Witcher is more niche than Dragon Age will ever be. I personally like Geralt for being a fleshed out personality, based on existing lore from books, and think that this approach of a set character is just fine. Better than a hollow, lame Hawke at least. But, Geralt is really not everyone's cup of coffee, I certainly can't much identify with him and doubt many others can. He is still interesting, but as much as I hate being the typical US Marine soldier guy in your average shooter, I can't get much into the scared macho Geralt is. For someone who wants to identify themselves with their role in a game fully, Geralt might appeal to some Metal-fans, but not to me, and I guess most female players will completely bail out. And still, Geralt is unique and from the set characters in RPGs that offer no choice still my favorite. But This is something Bioware shouldn't do, in Bioware games I like freedom in character creation. Hawke was already too much to bear, gender/look choice or not. Because there wasn't enough character depth, which Geralt has, so at least that part could be an inspiration.
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Next we hop to the adult stuff in The Witcher. Personally I like adult games having adult content, as long as the presentation is good. I don't need pixelporn, but I don't want to be treated like a kid. Many say The Witcher 2 did that part great, I tend to disagree. I don't mind nipples or full nudity, the "boobs scene" from the dungeon trailer for example is quite alright.
But Geralt isn't sexy and watching him taking his love interest doggy-style isn't really what I have to see. It's a matter of personal taste, I just don't find it very sexy/erotic, more soft-pornish and I can see why many people don't like it. Bioware is the other extreme, the love scenes are just ridiculous and ruin the immersion from the other side of the spectrum. One word: Undies. I freely admit I used a decent-made nude patch just to be able to bear the Dragon Age: Origins love scenes without snorting my coffee over the keyboard. If you're not offended by nipples, I suggest trying it out, with a - good - nude patch the Origin love scenes mark the perfect middle way for me. Dragon Age 2 though is beyond help, not only for the ridiculous undies, but also the awkward animations. See Merill.
Otherwise, Mass Effect 1's love scene was still very well made. The story around it way to childish, but graphically as good as perfect. And even without undies there's nothing that would in any way offend anyone who doesn't want to see nipples or whatever. Perfect way to avoid both self-censorship and outcries from parents. If it hadn't been for FOX, but that's another topic.
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While being at adult stuff, to the point of gender equality and sexual preferences. I do like realism here, and the "we're all bi" way of Dragon Age 2 was one of the biggest mistakes when it comes to romances and stuff. Let me be clear here, I'd call myself a feminist and I enjoy bi-romances too, and I think gay options and all that are not only perfectly fine, but a must in a modern game. But please, not that way, it's one step to Skyrim's lifeless bot companions because it takes away their character and soul. Dragon Age: Origins made it perfect. I adore Morrigan, if she had been an option for a female player I would've romanced her, but she wasn't and that only improved her character and made her NOT a player bot. Realism for me is that there are some options, and some are not available. Lelianna was perfectly believable as a bi character, I know enough girls like that in real life, and then there's Morrigan who's die-hard straight and that must exist too. Hell, you can even find a believable middleway I think, which could actually improve the character. What a great achievement would it be for a gay player if they made the companion discover that other side of their sexuality slowly, after long work, instead of simply throwing themselves at everything that can't run fast enough?
I personally also like the same kind of realism when it comes to gender equality. Out in the world are many haters, people who think women belong to the kitchen and being gay is a sickness. Implementing this into a game and yet giving the player the option to succeed as a gay woman could open up so many new opportunities for great storylines, and the reward in the end for fighting the odds and showing all the zealots would be much more meaningful. In a world where every NPC is political correct and shrugs their shoulders when you are into animals or nekrophelia all those relationships are meaningless and unromantic. My view. If I ever finished my NWN2 PW, I'd add a hell lot of racism and sexism to make my own playing of a subject to those things more meaningful.
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Back to TW
What made the Witcher really unique and an example for other developers was the sheer love for detail. When I played Witcher 1 the first time, I almost had tears in my eyes when I just stood around looking at all the lovely details in the world. A cat licking it's paws in the tavern window, pidgeons flying up when you walk by, the NPCs hiding from rain and complaining about the weather. It was lovely.
Another thing I enjoyed very much were many down-to-earth side quests that were based on folklore. Not always the "get that big fat boss with his fancy magic" type of thing.
Many things in the Witcher were more low-key and not superhero stuff, which I'm quite sick of. Geralt is never the greatest hero on earth the kings bow to, on the contrary he's often met with suspician or open hate. I like the "you're character is no Popstar" approach and this is definitely I want more in Bioware games too.
This is actually something Bioware already did okay in Mass Effect 2. ME1 annoyed me big time with it's typical military/save the universe plot, while ME2's Shephard plays a lot more to my liking.
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Which brings me to Skyrim.
If there's one thing Bioware should really not look at it's Bethesda's writing, and the above mentioned superhero stuff. Seriously, I enjoyed Skyrim a lot in the beginning, but when I was made leader of a dozen guilds, including being named archmage even though my character can barely cast a cantrip, I stopped playing. Skyrim's writing and that superhero thing annoys me to no end, and it's really nothing anyone should take an example of. Bethesda's games always suffered from sub-par dialogues and storylines and the companions are an insult to any RPer because they are lifeless bots. You can easily blame the open world design and say "you can't expect better writing in such a game", but Obsidian proved the opposite in New Vegas, with enjoyable sidequest and great companions (still like Felicia Day as Veronica much more than Talis!). Sure, the plot still lacks, but it's a vast improvement over the standard Bethesda ware.
What Bethesda really does good again is the love for detail, and comparing Skyrim's junk laying around in the world being useable is the total opposite to Dragon Age 2's or Mass Effect's loveless loot nobody cares about.
Also, it's one of the few games where NPCs actually react to looting their houses! Hell, give me that. Not much to say about general world design, screenshots speak for themselves. But all that doesn't make up for a good story.
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A few more short things:
Day/night cycles and shops. I agree with Mike Laidlaw that waiting for a shop to open is one thing I can live without. I hate that on NWN PWs. Skyrim/Fallout's solution is well enough, the wait for X hours thing, but I'd also consider 24/7 shops with different shifts a valid compromise. If both isn't possible, I'd prefer open shops, simply for playability. And Skyrim was going to far with realism when it comes to the shop stocks too as somebody said before. Selling stuff in Skyrim is a tiring chore.
John Epler: Refering to Stalker makes total sense to me, I always look into a wide range of games for inspiration and Stalker gave me quite a bit of it. It's quasi-open world desing with borders was very well done, and I liked a lot more about the game when it comes to atmosphere and world design. What I didn't like by the way, and I noticed that only after finishing the game: The complete lack of females. There is no single female character in the whole game series! Well, that's modern sexism.
Well, so far for my rambling, ignore me and continue if TL;DR