Its funny you say the GTA series even though GTA V isn't even on PC. Also all those other series you said except for Total War, sims, and Company of heros is on consoles… I only play PC only games on PC. All valve games, CS games, and urban terror work on PC. So I don't care about any of those games.
Yes, it doesn't play all games but it plays 90% of them. I can play games like BF3 and MoH Warfighter fine. It probably just has to do with you having a shitty computer lol. Also if linux is bad why did a steam person say that the future of gaming for steam say its linux? They want people to use linux now and are supporting linux more and more.
You don't have to use windows to run games. Theres a free program called wine "wine is not (a) emulator" which allows you to run all windows games on linux. Also there are plenty of linux made games like TF2, Counter strike, urban terror, etc.
The beauty is, you don't need to know much of anything. Ubuntu is one of those Operating Systems that basically does it for you. There are some learning curves such as installing software that's not in the Software Center but most anything you need can be found there or you can find if in repositories online. Then you will need to use the terminal but there's a lot of tutorials online. I personally just copy and paste anything I need to do in the terminal….which isn't a lot.