So... The majority opinion was that it was epic, but...
I'll be one of the first to say that I was disappointed. Not many other people will agree with me, but I'm going to post my opinions anyway.
So, I loved the first part of the episode with Jun and the White Lotus, but the rest of it just... fell.
1. The Aang/Ozai fight. I know powering up and special effects are cool for the most part, but when he and Ozai started flying around the stage, I lost my suspension of disbelief. It was the main focus of the show, but I couldn't get myself to connect with it at all. They didn't explain why hitting the scar opened up the seventh chakra, especially since he still feels his attachment towards Katara, and the whole locking-away-someone's-bending thing was set up so shoddily it reeked of Deus Ex Machina. It was actually so boring that I felt like fast-forwarding through the whole thing, but I was watching it live so I couldn't. It also didn't help that the battlefield looked totally unrealistic but...
2. Music during the Zuko/Azula fight. (EDIT: This one bothered me the least, but it still differs from a lot of other people's opinions...) The music matched the whole Azula-is-going-crazy-so-we-should-feel-sad-for-her thing, but overall it took me out of the episode and made the fight scene seem stiff. Instead of getting caught up the emotions and intensity of the fight, I calmly sat back and waited for the dramatic shot that the dramatic music was leading up to.
3. Where did everyone go? One of the reasons I loved the first two episodes of the finale was because it had other people in it. The avatar world still consisted of more people than just the main characters. And I loved the other season finales and the DoBS was because they brought back characters/had them interact in ways never before and included them in the main plot. After the first two episodes and the finale battles began though, everyone except for Azula, Ozai, and the Gaang disappeared, and they didn't reappear until the finale three minutes. I know it was probably to make the viewers focus more on the main characters, but it just made me wonder about the others. (Like how Teo, the Duke, and Haru were included in the Gaang just to be background noise until they were written out again.)
4. Zuko's mom. Everyone's been saying this, but WHERE IS SHE? It's been hinted at time and time again, and it just didn't feel like Mike and Bryan to leave it hanging. Sure, some people have said they could do a new season where they find her, but they don't new a new season. There were plenty of filler episodes in the story that could have been cut to include something more plot relevant. (The cutting of filler episodes also applies to the whole locking-away-someone's-bending thing as well.)
5. Ty Lee and Mai. Everything up to and including the Boiling Rock was pushing them into the direction of becoming a bigger part of the story. I like Maiko almost as much as I like Zutara, but the way that they only included them at the end felt really really forced. Like I said in another comment, it's like the creators forgot they existed and with three minutes left they said, "Hey wait. We need to bring her back so she and Zuko can make out again."
6. Iroh's Spirit World Journey. Iroh's been to the spirit world. This has been brought up multiple times throughout the seasons. It's never been explained. Sure, it let's fans come up with their own theories, but I think it would have been kind of important in Iroh's development as a person. Since I think it's related to the White Lotus Society, I think it could have been brought up. Also, the White Lotus Society was never explain other than it being the society to which all the awesome Avatar old people belong to... which is cooler. But it would have been cooler if they actually explained how it functioned somewhat.
7. Other things never quite explained. Combustion Man will forever remain a mystery. Toph's crush on Sokka and her relationship with her parents will be left up to fans. We'll never actually know what happened that night Azulon died. (Yes, we have Ozai's and Azula's accounts, but they're not the most trustworthy people.) Smellerbee and Longshot must be still trapped in Lake Laogai. Etc...
There were a lot of other parts that annoyed me, but these are the ones I can remember. Don't get me wrong. There were still awesome parts about it, and I just loved the first half... it's just... It's not as epic to me as it is to other people. The second season finale remains my favorite. Feel free to agree with me, bash me, or say I'm taking a children's show way too seriously.