Ultima 8 - Many Ultima fans disliked this in the series as it didn't follow on elements from prior games. But I, having no experience in earlier games & thus no expectations, found it thoroughly enjoyable & absorbing. The story was quite entertaining, what with the old deieties & strange monsters. The open-world experience was new to me, and opened my mind to the idea of a virtual world. I loved the unexpected interactivity of many items within the game, as well as the little puzzles found throughout the seemingly gigantic map. These elements combined with the open-world aspect was something I've always wanted to recreate & relive... in some form, in my very own interpretation & storyline. Today I have the ability to create graphics that at least partially achieves my objective. I believe that one day I will accomplish this feat.
Ultima Online - Using the same engine as Ultima 8, I found it really easy to get into. This was the game that changed my life. Played it for 4-5 years or so I think. During the final two years, I strived to earn all that I ever wanted from the game before finally letting it go. I trained one of my characters to have one of the most powerful skills in the game (at the time), I single-handedly earned enough gold to purchase the third largest player-owned structure in the game (despite the hyper-inflation going on), and I came full circle with my guildmates (where previously I would die from their 'unexpected' sparring, towards the end I repeatedly rescued them from their clumsy gameplay). But those were just things anyone would be expected to do and achieve for being in the game for so long. They weren't as important as the lessons I learnt from playing the game, lessons I would probably remember for the rest of my life.
There were other games too that game me nostalgic feelings, like Doom 1 & 2, Wolf3D, Chaos Engine, heck even those old QBasic games like Nibbles & Gorillas. But I don't fondly remember those as well as the above two games.