The introduction to the storyline really does start off great. The zones are massive and have some impressive detail, but certain areas feel convoluted and frustrating to navigate. The classes feel about the same from a gameplay perspective, however there are severe balancing issues that unfortunately blizzard only allowed early access players to take advantage of. Dungeons are being blown through like the monsters are made of paper, and mechanics are too forgiving early on.
The real let down however is the story. While it does start off great, the overall arc is extremely repetitive and the narrative veers away from the player and focuses on the new paragon NPC's they've created. This results in minimal character development and tired themes we've seen replayed over and over again with no real investment in the story.The real stagnation happens later on, where you can finish the story well before hitting 80, leaving you little else to do but finish up doing the blow through dungeons, Torghast (Opps! I mean delves without the power ups.) and world quests.
All in all, the start of The War Within is lackluster. But if you can push through the dredge of clearing the story and getting to 80, you don't have to worry about clearing the story again and can level other characters through dungeons and world quests. But fair warning, that does get old, pretty fast. As nothing particularly new has been introduced to the game.