Many game development companies are less formal in terms of workplace attire than other types of software development houses. For example, I know that one place at which I will be interviewing soon has a predominant workplace culture of jeans and polos or t-shirts.
Should I wear a suit? Shirt and tie? Shirt and sport jacket, with or without tie? I want to show that I'm serious about the job, but that I understand the culture, too.
As with a lot of hiring questions, "it depends". The human element in hiring can't be ignored.
That being said, there are a couple of things to keep in mind.
Are you going to be talking to a big company or a small one? Bigger companies might have HR personnel who aren't necessarily game developers who do the initial filtering. They might be more inclined to look at appearances for their opinions on candidates than, say, the art director at a small company simply because they don't have the expertise to really look analytically at someone's portfolio.
Also, remember just like any other job you're going to be working side by side with people for (hopefully) a long period of time. First impressions matter. As an interviewer I'm looking for both game development skills and people skills. Namely, am I going to want to work side-by-side with whoever I'm talking to? Do they show poor judgement (like wearing an offensive t-shirt to a professional setting where they don't know the audience)? How's their hygiene? Dressing sharper might help with those sides of things.
But don't dress sharp if you don't know how. Don't wear a button down shirt that isn't ironed. Don't put on too much cologne. And if you're not comfortable in a tie, don't wear one. An interview is stressful enough as it is, and you don't want your clothes working against you.
I've interviewed junior candidates that wore suits and ties. If we thought they were smart (and likely to get the job), we'd poke fun at them a bit. Mainly just to get the point across that our culture didn't really care about that kind of thing (and, as far as I know, most game companies really don't care). But generally it didn't count against them.
Find out how people generally dress there. Dress one step fancier than that.
Personally, I feel that you should always convey a professional image. You don't have to be completely suited and booted, but you should at least make an effort to wear an ironed shirt and some smart trousers. Regardless of whether you have a small or large games company, even if the culture is to work in T-shirts and jeans, like it is as my place (and many other games companies), first impressions count.
You don't know who is going to interview you, and it's not always possible to find out exactly how people dress at the company you're going to, so it's always best to paint yourself in a positive light.
Other general tips for interviews:
There isn't a "it depends" on company. You don't get hired based on what you wear, so wear the standard interview gear (e.g. dress shirt, tie and dress shoes). This is universally accepted by all companies and dressing otherwise is running the risk of "it depends" on company.
Easy answer: when you are offered the interview in the first place, ask how they prefer applicants to dress! If you forget, you can always call/email your contact at that company and ask in advance. It's a reasonable question and you don't lose points for asking.
The good news is that the game industry is mostly a meritocracy. I personally like to wear a suit and tie for the interview (it was just drilled into me when I was young to always always always do this), I usually get some gentle ribbing about how I'd better not show up to work looking like that, and then we get down to actually figuring out whether I'm a good fit for the position. I have plenty of colleagues who "dress down" and get hired that way, too.
Ultimately, a hire / don't hire decision is going to come down to your skills, abilities, and fit. I have never, NEVER heard of anyone in the game industry getting (or not getting) a job solely because they did or didn't wear a suit. (I suppose if you showed up wearing a t-shirt with an offensive image on it that would count against you, or if you showed up wearing nothing but a Speedo or something, but accounting for basic common sense you should stress about showing why you're an awesome developer, not a snazzy dresser :)
In my admittedly limited experience (my previous job was at a game studio and I have a bunch of friends who work at different studios), game studios tend to be pretty casual. Personally, I wouldn't dress up past an ironed button-down and solid-colour, non-embellished jeans or dress pants for an interview at a game studio. They're generally places where people wear jeans and t-shirts to work, you're likely to look out of place and like you don't understand the culture if you dress up too much.
That said, it's just an interview and what you wear (as long as you're clean and presentable) doesn't matter as much as your skills, plus good interviewers understand when candidates overdress because they're worried about making a good impression.
Just like for any other job, dress as you would like to dress every day if you get the job.
You can't complain you have to wear a tie, if you wore one during your interview.
It does depend but the answer is very specific to the type of interview.
I never wear a tie for a software or tech company and no one ever shows up with them for interviews in the places I work unless they are from China or something like that. I just wear a nice dress shirt with a solid color, nice pants and dress shoes. Pretty close to how I show up to work. And that is how everyone else seems to show up as well.
For government work or trying to get a contract with a fortune 500 company you need to wear a dark, conservatively cut suit. You will look and feel horribly out of place in anything else. And be sure to act very polite and formal as well and don't be opinionated at all, which you can usually get away with a little at a software company so long as you are somewhat inline with the opinions of the locals - and if you are not, then maybe you should avoid working their anyway.
There's probably some places that won't care if you are less formal than option A) but I would not push my luck. You don't want to be seen as too eccentric.
As for hiring only on abilities goes - ha. Some fantasy world. People are not so objective as that even at the best tech companies. Not to mention they are only able to judge that within their own abilities. And not the abilities of the best programmer there but of the upper management who are usually a whole different ball of wax compared to their top tech guys.
