Team Fortress 2 is one of my favorite games of all time.

TF2 is fairly unique in its utter dsregard for long term progression.  A long time fps player new to TF2 might often win against an experienced tf2 player with less twitch capability.  Tf2 favors moment to moment reactions a situational awarness.  This focus has shifted slightly as TF2 has aged, with so many alternative weapons surfacing, there is often a better weapon than the stock for each situation, which you only have if you have spent a lot of time or money aquiring them.  Therefore the aquisition of items becomes a progression of sorts.

TF2's design and evolution is, to me, like building a boat:  At first, you have very few materials, say 9 planks of wood.  You lash them together as best you can.  Each plank is carefully balanced with the others.  They must be bound very tightly, or else water will get through.  That boat was tf2 at launch: tightly balanced, fast and fun.  As the years have turned, valve has continued to add more and more wood, each subsequent piece less and less critical to the integrity of the ship.  There is just so much boat to stand on now that it would be increasingly difficult to un-balance it.  Each update adds mass to the existing balance, and additional quarters for the new free-to-play crew to explore.