I believe what was being said that nothing changed post-ending. The game, environment, and atmosphere are virtually identical.
MASSIVE END-GAME SPOILERS****
Dragons still fly around, no-one seems to ever acknowledge what you did, no new mechanics are introduced to celebrate, no one really talks about the aftermath of the civil war (or any quest-line for that matter beyond owning a house and one or two lines of random dialog. I believe I killed 5,000 Thalmor agents and 20,000 Stormcloaks, so why are they still around?). Apart from guard comments and dragons I’d scarcely say the beginning of the game is indistinguishable from the end of a 100% completion run.
To change that a few things could have been done.
1: Give the player a quest-line to reunify former Stormcloak and Imperial supporters, rebuild cities, and new random and unique encounters.
2: Make all four quest-lines similar to the end-rewards of the Dark Brotherhood. In that you got a player-home that could be fully furnished, quests, and a ton of atmosphere. Compare that to a new axe, armor and a choice of three spells, or the staff of Mangus and they just seem underwhelming. Let the player make his own spells at the end of the college quest-line, recall him to defend the shrine and buy-out and run businesses and luxury estates at the end of the thieves quest-line, and something cool at the end of the companion quest-line. Give the end something to them.
- Give the player the ability to significantly alter Skyrim at the end of the main-quest. Be it found a castle as its Lord, hunt down the dragons to extinction, or other-post quest activities that showcase the player’s newfound position of influence. Apart from the ability to shout, dragons flying about, and a few lines of random banter you have nothing to show for completing the MQ.
****MASSIVE END-GAME SPOILERS