Can I continue to play after the game ends?

  1. Yes you can, you can continue playing and complete all the side quests.
  2. There are no really significant changes like in Oblivion. For example even the dragons will still be around for you to hunt down. Without giving to much away, one of the small things that change is that NPCs will sometimes comment on your achievements during the main quest.

Yes you can, there are many quests to do outside of the main quest line and don't worry te game is still just as fun, to be honest some of the other quest lines seemed as good or better than the main game.