What makes Dark Souls good to me at least is the atmosphere, the game is absolutely dripping with it and its easily one of the (to use a buzzword) most immersive games I've ever played. The atmosphere infuses every part of it, from the tense combat to the scraps of lore you can find and so on. The combat is another high point, its much more reliant on patience, preparedness and caution than other games but its very rewarding to push through a section. Finally the games approach to story and lore is really interesting, and a big part of why people are still talking about the game so long after its release, its everywhere in the environments, item descriptions, enemy placements, and all manner of other details; however the game doesn't outright tell you much of it so you're left to piece it together yourself and form your own interpretation of it. This combined with the quality of the lore itself, the beautiful art in the game, and the atmosphere gives the game a very 'mythic' feel to it, something I haven't seen in many other games.
As for tips to playing it I honestly think its best to figure it out yourself, Dark Souls is a hard teacher but its very rewarding to piece things together yourself. That said in general be patient, cautious, and observant and you'll go far. Also while I don't recommend using a wiki on your first playthrough there are a few things like covenants and embers that you'll probably want to look up, as the game could stand to give you some guidance in places.