Was thinking to add a replayable scenes feature to the game
This could be interesting, especially if it's a sandbox game, but it's not necessarily something easy to do ; at least not easy to do well.
Should I include other characters thoughts in this ? (I could also put it as a feature to turn on/off if people want to see other characters thoughts or not)
You shouldn't even include the MC thoughts in it. They should be shown to the player, whatever through the dialog or the visual, not fed to him ; this as much as possible. Depending of your own skills, it's not always avoidable, but it should be limited to the strict minimal.
In real life we don't read mind. In place, we interpret the reactions of the person, and try to read through what this person say. The same should be done in a game. This especially since you have something that book writers don't have, the visual. It's a big help since if a character is, by example, annoyed by what the MC said, making it frown can be enough to change the tone with which the player will read its next dialog line.
Yet, even in books, you never have more than the MC thoughts. Never you know the thoughts of others characters.
what are people's thoughts on maybe playing certain parts of the story also from a second perspective?
It totally depend of the story, the way you want the player to approach the game, what you mean by "second perspective", and what scenes are concerned by this.
Firstly the story need to permit this, what isn't always the case.
Secondly, it will obviously hurt the immersion, so it don't necessarily fit with a first person POV. Even with a third person POV, it will not works if you want your story and game to be immersive.
Thirdly, if it's to show use the scene a second time, but from the point of view of another involved character, it's totally useless. The only real difference would be the thoughts of this character, and like I said above, it's something to avoid. It will also show the visual reaction of the MC, but if you need this to show them, then there's a problem since it should be shown in its dialog lines. Plus, you apparently initially intended to show us his thoughts.
Fourthly, and it's the only "do it" point of this list, it can be interesting if it's "meanwhile" scenes. As I said, it will hurt the immersion, since the player will know more than the MC, but it's one of the many ways to avoid having to show a character thoughts. Take the classical "the MC is catch peeping at his mother in the shower". Instead of having a thought line for the mother that would goes like, "oh my god, my son is peeping at me when I'm naked. It's so hot...", you can left the MC at what he's doing, and showing us that, "meanwhile", the mother is in her room, masturbating while whispering her son's name. What can also be done without second perspective, by making the MC pass in front of his mother's bedroom door and hearing her moan like crazy, having the feeling that he sometimes heard his name. Up to you to decide if the "hot" (first option) is more important than the immersion (second option).
What are the preferred graphic styles when it comes to 3dcg ? I've seen a lot of games with good graphics but different styles. Which ones are preferred?
Hum, there isn't this much games with effectively "good graphics".
This said, the graphic style don't matter, as long as it fit the story. If, by example, you try to write a serious story and use a cartoon shader it will not works.
As for "good practice" here, don't use things out of the box. It will imply more works for you, but having a character that is yours, even if you just used the basic morphs to change few things here and there, will always be better than having the same girl than this game, and that one, without forgetting this one and, wait, isn't also the same in that game ?
Also use the fit morphs every time it's possible. Whatever if it's not perfect, having clothes that follow physics and not every single curve of the body will always be more enjoyable for the player. And try to have lighting consistent with the scene.
Globally speaking, you should pass from one week to more than one month (depending of your skills) preparing the visual part. Firstly by morphing each characters until you've something enough "unique looking". Secondly by testing each character in each locations you'll use, while in the same time working the main lighting you'll have for those locations. Doing this, you'll quickly discover that a character that looks good in one location, under one lighting, will suddenly looks like shit in another locations, or under another lighting.
Do this and then, whatever if your rendering skills are average, your CGs, and so your game, will looks better that most of the others.
How important are animations and how good do they have to be?
Not this important. They can really add a lot of life in your game, but only if they are near to perfect and put at the right place. Except for sex scenes (yet it depend some can be really bad), no animations at all will always be better than a not good enough one.
There's one game I forgot the name, that tried to use animations. One of the first you see is a girl walking... like a horse (you know, when they move slowly, showing every step of the move), and needing something like twenty steps and five seconds to reach the door that was 2 meters away. It was so ridiculous that it totally killed the game for me.
How important are music and sounds to a game experience?
Not at all (I tend you listen to my own music while playing) to fundamental. It depend of the reason why you use them.
Regarding music, take an iconic scene, Dark Vador first appearance in
A New Hope. Remove the music, and the scene is flat. A French filmmaker recently said that "[he] love when the music know about something that haven't happened yet", and it's something that any dev should keep in mind if he add music to his game ; the music is here to set the mood.
Think about "regular" games, and this moment when the combat music start, but you're still alone. Fear, or excitation it depend, sometimes even both, start to grow in you. Something big will happen, you know it, but you don't know what nor when. One second before you were casually walking, while thinking about things as unrelated to the game than, by example, your grocery list, but now you're fully awake, concentrated on the game, ready to fight for your life.
If it's used this way, if the music effectively add a dimension to the game, then yeah it's important. I'll even say that you need to explicitly say it to the players, in order for them to test if for once it's true (because alas the "the music is important in this game" are too often a lie), and so fully enjoy your game. But if it's just to put music, then do as you want, but know that many (perhaps even most) of the players will just mute it and listen to their own music.
As for the sounds, it depend what sound and what purpose. If it's to sound the sex scene, I'm tend to say, "forget about it". Sound is an important stimulus during sex, but in games it tend to be a turn off because it rarely fit the action. This mostly because it's fucking hard to do it. You don't know how many time the player will need to read the sentence, how many time he'll stay on a give image.
Therefore, either you'll loop your sound, and it will feel weird, or you brutally shut it, to pass to a more accurate one, what would feel even more weird. Or, what is generally used, you'll have a global sound for the whole scene, that will loop forever. Some can like it, but for me a woman going near to orgasm while I haven't even put it in, it's not something sexy. Same if the instant after being near to orgasm, she slowly moan because she's still not really at it. I prefer my girls to be silents, than them faking it.
Also, most devs who do this tend to use the same files for every sex scene. And once again, having different girls moaning in the exact same way with the exact same voice isn't at all a turn on for me.
As for other sound effects, it's used like for the music. Used well it can add some depth to the game, but you must know that not all the players will hear them, so they need to also reflect in the visual or dialogs. Like I said recently on this subject, if someone knock at the door, don't make the player jump to the door. Players who turned the sound off will not understand what happened, precisely because they didn't heard the "knock knock".
How important is the UI in this type of game ? What are some example of favorite UIs
They are 200% important, especially if you effectively go for a sandbox game.
Take a look at the difference between the original stats page of
Super Powered :
and the same information as shown by my mod :
The feeling the player will get totally depend of the UI. A good looking, intuitive and easy to use UI will always add something to your game. It's the same that what I said above regarding the renders, it can make your game stand over the mass even if the rest is average.
scene transitions - thoughts on that?
Natural and without useless effects. It's the most difficult part of a game, and also a movie. Once again It imply more works for you, but don't hesitate to add one or two additional CG in order to ease the transition and make it less, hmmm, rough ?
Will add more points if people have ideas on that
Just one thing to add: Go for what you feel.
The most important point in a game isn't everything you said above, but the passion you've for your game.
By itself it's not enough to make a hit, but it's what make the difference between two games that, globally, share the same story, the same game mechanism, and the same quality. Not only people can excuse many things from a dev that clearly do it with passion, but it's also generally felt while playing the game and it make it a little more enjoyable. And this, the player's enjoyment, is the most important point. You can make an average game, with a cheap story and use Sims for the CG, if you're passionate, if this passion is visible while playing, you'll find your public.
P.S. Should I add tags to this post like VB and RenPy ?
No. Even if you're planing to use Ren'py to make the game, what you ask are generic questions that apply whatever the engine.