Is it worth to buy the game and expansion for 20$ ? YES ! that is a steal for the amount of gameplay you get out of it.
There is no other hack n slash game on the market at the moment that comes even close to D3 combat. Smoothness of animations and details.
If you like to hack n slash through hordes of monsters, you will spend hours and hours @ D3.
Have you guys noticed one thing, all D3 forums are full of PoE players saying PoE is better and D3 is deader than dead. Yet no D3 player goes to PoE related websites to write bullshit.
D3 vs PoE:
Both games are great. They are different, provide you with different experience and gameplay. Some will enjoy one while others the other. Many play both.
To me D3 is superior because I enjoy combat the most, smoothness and pace. I play both games around a month after release of new season/league and after that I move on to something else like Grim Dawn. I got more than 8k hours spent @ D3 to date, around 5k in PoE.
People saying PoE is hardcore, complex, hard to learn etc. that was the truth like... 2 years ago, atm PoE gets easier and easier. You could show a total noob 1 youtube video of a top PoE meta build, provide him with items and he would run through from normal to top tier maps holding right mouse button. I for one hope PoE changes its direction and stops the casualization of the game.