World of Tanks (PC)
Actually played so much of this on Saturday, that I dreamt World of Tanks Sunday night, making for very poor sleep. Kept waking up. This has only happened to me once before when I was playing a lot of XCOM.
World of Warcraft (PC) [Never had the opportunity to experience an expansion from the start, always joined in the middle or at the end, so keen on trying this at least once]