What makes the TF2 art style so iconic?

Recently I finished creating 2 assets for a game and I thought "hmm, these kinda look like they're from TF2" and as a team fortress fan that got me wondering? what makes their design so iconic, what makes look ageless and nice, is it the lighting? the way the assets are made? the textures? and i am curious what some other people think since I would love to be able to have a similar style for my game