I'll provide a list of basic facts about x64:
1. x64 is FASTER - but only if you run everything that was made for it natively, and not an emulation. What does this mean?
Well, to run x64 code, you need both hardware and software support. Hardware means your CPU and Software here means your OS, the programming language of the said software, and the base code of the software itself. All of which must be made natively x64.
Cold hard fact: most software nowadays are for x32 only. So your CPU and OS may be x64 but when you run the software, it is actually an emulation. This doesn't offer you any speed advantage but consume more ram, this lead to point 2.
2. Due to the new address, software that were made to perform the same task will now consume more ram in x64. Put it simply, Notepad x32 will consume less ram than Notepad x64. Notepad x32 run on x64 OS will still consume more ram. This sounds like a disadvantage but it's actually not. I'll explain in Point 3.
3. Thanks to the new address, software are no longer be limit at 4GB of RAM. This include the OS and the ability of the software itself to be able to use more than 4GB of RAM. For example, if your windows is x64 and you have more than 4GB of RAM, your windows can take advantage of it. Now you may raise a question: Aside OS, what else could possibly need more than 4GB of RAM?
Many modern software nowadays require more than 4GB to run better, this is actually a godsend to those specialized software. For consumers, it's Graphic & Video Editings software, some Analysis or Accounting software that require to process a huge amount of data, and Gaming. For enterprises and infrastructure, it's all about webserver, database server that would need way more than mere 4GB (oftenly 32GB, 64GB, 256GB, and even more), visualization engine and many more custom web application such as facebook, twitter, gmail, evernote etc... they all have a back-end engine and use massive amount of ram.
Not only does x64 software can use more ram as necessary, it also runs much faster, from 30% to 200% faster than the x32 counterpart. While it does use more ram as outlined in point 3, the disadvantage is quite insignificant for those who really need it.
So once again, to take advantage of x64 bit, you gonna need: the hardware - CPU must have 64 bit instruction (AMD64 or INTEL64), the Mainboard support is not applicable you cannot use a cpu inside an unsupported mainboard, your OS must be x64, and your software must also be x64 native. You can have less than 4GB of ram and still taking advantage of x64 processing power but for best performance - you need as much ram as your application demand.
To answer your question, most hentai game are x32, and will run under x64 OS just fine since OS can run x32 software in an emulation. For low level access driver however, this may not always work.