I am fairly new myself, but I will give you my impressions where I can.
In general, I'll say right off, if you are heavily tied to any proprietary Windows programs, you should, sorry to say, stick with Windows. I don't know what version you are running, but I have a lot of experience with Windows 7, and it's awesome. It's fast, easy to use, and very stable. And it just works with all those Windows programs, it will even find an load drivers when you need them, all that stuff. I don't want to chase you from Linux, but you should know that even at it's best Linux does not fit easily in a Windows-dominated world. You will have to make a lot of adjustments, and do a lot of work.
As far as your specific questions go, I'll start with one you didn't ask, but which is implied. In my experience, LibreOffice *will* open Microsoft Office files, and will save in that format, but it is most definitely NOT like opening these in Microsoft Office, at least for Word and Excel. The file will look very different, and in many cases a lot of the formatting will not transfer from Microsoft Office to LibreOffice, and files saved by LibreOffice in the Office format will not be readable by Office. If you have very simple files, with little formatting, you will probably be ok, but (again, in my experience) even working between Office on Windows and Office on Mac things look different, so imagine going to a completely different program which is trying to open and save proprietary files. I will have to say I have at time been able to get Office itself to somewhat work in a Linux environment called WINE, but that is not particularly easy or stable, eiether.
With iTunes, I am told you can get it to work with WINE, except for anything that involves connecting to Apple. You can't do that. And, though you can play things you bought from iTunes in several different Linux players, in my experience, you can't make a CD of anything from Apple. Maybe you can transfer songs you already have to your iPod, I don't know about that, but you will not be buying any new ones or using whatever they call the iTunes cloud in Linux, I am pretty sure.
I don't know about the game. I do know that Linux is notorious for not supporting 3D video, as the drivers are proprietary, so they have to reverse engineer them. You can get proprietary drivers, but it can be a huge amount of work to get them to work (Linux Mint does a great job at that, by the way). I 'play' second life, and the only distro that I have found that works with my computer to do that is Mint, and it's not like I just gave up right off with the other distros--I have spent months researching and posting trying to figure out how to make it work in something other than Mint.
I know this isn't a glowing endorsement of Linux, but really you have to be committed to sticking with it and making it work. It isn't a direct replacement for Windows in the least. There are a lot of rewards, or I wouldn't be investing so much time in using it. But if you want something that does everything you are used to doing with same amount of effort that Windows takes, you will be very disappointed and frustrated. However, if you choose to do it, there are a lot resources to help you. As remoulder said, all the common things, and most of the uncommon ones are covered somewhere either in the Mint Forums, or elsewhere online. And, failing that, or if you are confused by what you find, if you show you have done some research, people will generally help you.