The first thing that comes to mind was my first play through of Yakuza 0. Majima spends so much time winning stuffed animals for a little girl that lost her dad. Part way through the quest line she starts calling him dad and it made him so happy. It warms the heart and I could not stop smiling.
Right at the beginning of Nier Automata when it shifts into a bullet hell game for a bit and the already amazing soundtrack changes styles to match I just knew I was in for an amazing experience.
Recently, Hi-Fi Rush made me smile (and laugh) more than once :)
Finally beating the asylum demon on my very first playthrough of dark souls.
Then i immediately realized i only just beat the tutorial.
Playing Dark Souls 1 for the first time has so many amazing moments like that - finally defeating the Bell Gargoyles, or surmounting Sens Fortress and pushing the Iron Golem off… But I don’t think anything will ever compare to the exhilaration I felt in beating Ornstein and Smough for the first time.
