Not a unique opinion, but Portal is probably the closest thing to a perfect game. Nothing feels unnecessary, and every part of it (story, gameplay, visuals) is not only good on its own, but also work together to make the game better than the sum of its parts.
Portal 2’s also great but suffers from a lot of fluff imo. The analogy I like to use is Portal 2 is like a big feast of really good food, while Portal 1 is just one small dish, but it’s the best version of that dish you’ve ever tasted.