If you are wondering if you should give this show a try, I'd say go for it. Granted, I didn't care for it as much as other people did, but I realize I'm definitely in the minority.

Liked:
1) Dr. Kim was SO MUCH more likeable this season. I didn't care for him at all in season 1.
2) Overall, the acting was better this season. A lot of overacting in season 1. I still didn't care for the acting/character of Im Won Hee as Jang Gi Tae. In everything I've seen him in, he's always too over-the-top.
3) Liked the storyline of Woo Jin and Eun Jae. I liked how they did the flashbacks to them in college. I know this is a medical show and not a romance, but I would have liked to see more of them. It's hard to imagine that much beauty in one place.
4) They spent a little more time with some of the patients in this season, which I appreciated. The more you see a bit of a backstory, the more you can relate. to them and care about them. Case in point, the pregnant woman in the bus accident.
I was glad that they cut down a little bit on the number of times they performed CPR on the patients.
5) Thank you for more screen time for Kim Min Jae. His relationship with Ah Reum was cute, but unnecessary, and pretty unfulfilling.
6) The thugs that owed Eun Jae a favor. They showed a little bit of heart to counteract the over-abundance of bad guys.
7) The writers really developed the Doldam staff's characters, which made me like them and root for them. In this season, I was able to see why they wanted to work there and with each other. I didn't feel the bonding in season 1.
8) Kim Joo Heon as Min Guk - I loved to hate him. Granted, the man seriously needed some therapy, but the actor did a great job of portraying the character's long-standing insecurities and strong at-any-cost ambition (SPOILER - I LOVED that they turned this character around)

Not so much:
1) Oh my gosh, EVERYONE was eavesdropping on everyone else! Someone suggested making a drinking game of it (brilliant idea), but you'd be taking a drink about every five minutes. And what is the point of offices with doors in you can actually hear everything through them? It just made everyone look unprofessional. Add to that the number of people that read stuff on or in other people's desks. Just wow.
2) How many bad guys does one show need!?! The main bad guy returned from season 1, evidently with no repercussions for what he'd done in the past and really, I was never really clear on what his purpose was. He acted like a petulant child that wanted to play with a toy that someone else was playing with. Thankfully, he won't be back in season 3. The lackey that worked for Min Guk, he was just so slimy I had to fast forward through his scenes.
3) Eun Jae's problems with being in surgery - passing out/vomiting. I had multiple problems with this. First, this seemed like a deep-seated thing stemming from the fact that she didn't actually want to go into medicine (I mean, her conversation with her mother, yikes!). Popping anti-anxiety medications like candy right before surgery? No one with any sense of responsibility would do that. She needed to get into some therapy. Then her getting some medication from Dr. Kim and not even caring about what she was taking? She never questioned him about what the pills were. Then, she went around telling everyone she was fine because of the pills that Dr. Kim had given her. This is something that would have gotten them BOTH in trouble. And to have it turn out that she was just taking digestive enzymes? The whole thing was too implausible.
4) Again, bringing people from the main hospital and they only want to do the work they want to do.
5) Do In Bum - he comes back after three years, he still has a locker, and he goes into surgery right away?! He was there to investigate something, not do surgery. I was glad that the antagonism between him and Woo Jin didn't last long, we had enough other people constantly antagonizing others.
6) Doctor Kim still doing surgery. That's a lawsuit waiting to happen.
7) What was with the Harry Potter Music!?!?!