I would suggest Rouge-likes if you like the Free-roam kind, im not sure if your processor can handle some of the more advanced ones, but ill list them anyway.
Powder- My first one, loved it, while its not all that easy its tons of fun, its also very simple compared to most others.4
Dwarf Fortress: Adventure mode- A bit complex, and VERY demanding of resources at times, but its combat system is tops and it features a massive open world thats randomly generated, along with its own generated history, heroes, myths and ancient beasts.
Cataclysm- Its actually Cataclysm Dark Days Ahead, its still in development but a lot of it is done and it features quite a few advanced mechanics, be aware, this one has a lot of content, but it takes a LONG time to get to it. Learning how to properly fire a gun or butcher meat will take at least an in-game week. Never the less hacking systems or installing bionics and building cars.
I recommend more as I find them.