Also consider your audience. If you are a gamer then you probably looking at making the type of game that you would like to play but, the market on mobile devices is entirely different than the market for PC and console.
The games that do well on mobile are puzzle games like Angry Birds and time based multiplayer cow clickers like Clash of Clans. That isn't to say that you couldn't have a little success with a 2D strategy game but, the chances of it becoming visible are very small.

Indeed mobile is just about the harshest platform to think about right now. The barrier to entry (aside from a miracle hit) is enormous.

Cost of production of a good app is somewhat steep (definitely lower than consoles though, but compared to a web-based game...)

The real issue is getting noticed in the millions of games on the stores. You're not going to make top 100 and need to have a means to drive traffic to your game through some other way.

Quite honestly, I've worked with some of the top names in this industry and they're even struggling on the mobile market with the majority of their titles, relying on their few hits to finance the rest of their development. Unless you plan on releasing 30+ games in the next 1 or 2 years, mobile is probably not a good idea unless you're lucky.

Then again, that's my personal opinion.

(of course, if you make, say, a PC game in Unity, and all it takes to port it to mobile is a new control scheme and adapt your UI and that you had planned for this, then publishing it ALSO on mobile can't hurt, and you might get exposure on mobile from your PC users, so why not?)

(of course, if you make, say, a PC game in Unity, and all it takes to port it to mobile is a new control scheme and adapt your UI and that you had planned for this, then publishing it ALSO on mobile can't hurt, and you might get exposure on mobile from your PC users, so why not?)

Well, it certainly is worth a short try and a cheap to produce prototype, but for most games, the statement that "building for mobile is just a click on the build button away" is not true. Even with a new control scheme, and the whole game planned around it (the graphics and game logic not depending on desktop like performance and whatnot), there are many other tasks to perform.

Testing for mobile must take the top seat, if you ignore marketing and publishing. Might be not too hard on iOS, but for the myriads of Android handsets and tablets and consoles out there, that is going to be either a nightmare, or you will have to release your game in a state tested on only 0.1% of the total amount of different devices out in the wild. Also not the best option as you can be guaranteed that on some device, there will be issues. And these issues will end up as negative comments in your app store review section... in the best case (in the worst cae, no comments will show up. Because nobody even bothered to download your game).

Even if you build your game for mobile in addition to PC or whatever is your main platform, and put it on the app store without the needed marketing push. What is the point? Nobody will find it, nobody will download it.

You might only have spent some days on the additional version, but the chance that this version generates additional revenue is slim.

Personally I'd say go for one platform at a time, and make the most of that. Really invest additional time in more marketing and better bugfixing and aftersales effort instead of trying to quick-cashgrab yet another platform. Your prime platform will suffer in the second case, while the additional platform most probably will do poorly as it is treated as an afterthought. While in the first case, your game might at least shine on one platform, while you can build a name for your game and studio that when you DO decide to release to a different platform down the line, a) you will be able to give the new platform the treatment needed to make your game also shine there, and b) your might already have a name from the earlier release on a different platform.

Also, never underestimate the effect of doing an additional release down the line can have. If your release for 5 platforms at the same time, you get news coverage once. If you are lucky, as your game still is an unknown factor at the time. If your release to each platform with some months in between, you have a chance to get news coverage 5 times... and MAYBE the later coverage will be more effective as your game no longer is unknown.

Well, it certainly is worth a short try and a cheap to produce prototype, but for most games, the statement that "building for mobile is just a click on the build button away" is not true. Even with a new control scheme, and the whole game planned around it (the graphics and game logic not depending on desktop like performance and whatnot), there are many other tasks to perform.

It's certainly not one click away, but on SOME completed products, it's much easier to adapt the input and UI work assuming it was build in a somewhat device-agnostic manner. It requires a means of doing things that infers a lot of experience however.

As an indie developer who released their first game, I was also toying with the idea of having my first game on mobile. But when I read the entire process to even have a smidge of a chance of being successful, I stuck to PC for the time being.

The responses here are very good as always, but I'd like to add a few more requirements to the list. Include soft-launching your product with analytics to ensure that your game has staying power, being really good with data or hiring a very expensive data analyst and finding out where your competitors are doing marketing.

The third one costs money, yes, and to have a chance of being successful. you need really strong marketing. Reddit and GameDev.net by themselves will not cut the mustard. You can't even do a KS campaign on a mobile game because KS is mainly PC-oriented, and KS is a great boost in addition to your marketing.

Release on PC first, get a following and enough capital to market your mobile game. Otherwise, as others said, you're very likely to get $0 on the overcrowded app stores.