BBC Sport pundits and former champions Stephen Hendry and Peter Ebdon reflect on the action so far and assess the business end of the event.
Pre-tournament favourite Judd Trump was beaten in the first round by 1000-1 title shot Rory McLeod in one of the biggest shocks in World Championship history. In his second-round match against Stephen Maguire, McLeod is 6-2 down after the first session.
Ebdon: "McLeod's victory was not so much of a shock or a surprise to me. I knew he would make it difficult for Trump and let us not underestimate what an incredible achievement it was for him, one that was fully deserved.
"There is only one player in that game that works harder than McLeod and that is Mark Selby, who is world number one. Rory has been my friend for over 30 years so I was absolutely delighted for him."
Hendry: "It has been an interesting tournament. All the main contenders except for Trump came through the first round so it is building up nicely.
"Everyone who should make the quarter-finals will be there so I am looking forward to the second week."
Five-time champion Ronnie O'Sullivan has produced some of his best snooker to beat Gary Wilson and then Shaun Murphy. He faces China's number one player Ding Junhui in the next round.
Hendry: "Ronnie has looked great on the table. I questioned in my interviews before the tournament whether he could win it or not and the way he was playing then, I did not think he could.
"He has not played well since the Masters but since he has been here he has looked really focussed, his game is very strong and he will be hard to stop. Ronnie is definitely one to beat.
"There is a difference between winning a match and winning the whole tournament. Ding edged through by beating Liang Wenbo but now has a huge match against O'Sullivan. You have to question whether he has it inside him to go all the way. That is debatable but his game is good enough. He has every aspect to do it."
Ebdon: "One of the things often overlooked is the pressure O'Sullivan is under, with the levels of expectation - the crowd, the commentators, millions of adoring fans watching at home.
"To carry that much pressure on your shoulders must be incredibly difficult and I cannot think of many other players in the game that could carry the mantle and the responsibility to the extent he does.
"He does a brilliant job, is a very gifted player and it was an excellent win against Shaun Murphy."
Four-time champion John Higgins came through a tough match against Mark Allen, while 25-year-old Kyren Wilson beat 2015 winner Stuart Bingham.
Ebdon: "Wilson did not hit top gear, he was feeling the pressure but that is what everyone goes through at the Crucible. Once he starts hitting the top gears, we will see something very special from him.
"Whether he has the experience to win this year, I am not certain. But he is good enough. He is a phenomenal talent, a great lad and his all-round game is very impressive.
"He is one of the best players I have played against. But we have not seen on the match table what I see in practice. He could go very close to winning it this year."
Hendry: "John Higgins is going to be very difficult to stop getting to the final. If they both go through, I can see a Higgins against Barry Hawkins semi-final."
The tournament is described as the "marathon of the mind" by former BBC commentator Clive Everton. Those players who have reached the quarter-finals have won 23 frames but still need to claim another 48 to lift the famous trophy.
Ebdon: "When you are concentrating so hard, it takes an awful lot out of you, you do use up a lot of nervous energy. We only have so much nervous energy for certain periods of time.
"This is one the reasons why the World Championship at the Crucible - lasting 17 days - is such a difficult and demanding tournament to win. You are really tested in all departments - physically, mentally, emotionally and spiritually. It is the ultimate test."
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The World Championship is already into its second week and there has been plenty of excitement so far at Sheffield's Crucible Theatre, which is celebrating its 40th anniversary of hosting the event.