Whoops, long-ish post ahead. Oh well.
Killua was made to be cold and distance ( trying to clone him as Hiei 2.0) with made up inner conflicts that were never part if manga Killua's character: guilt ridden by his background and a struggle to suppress his killer urges. That is not added layers in case thats what you are thinkin, that's a total change of the character's core. Not to mention 1999's character revision is corny and cliche as hell.
A simple, fun and revealing ball game in the manga that showed us how Gon and killua deal with the same event is utterly ruined by some chick and focused shifted to whitewash Killua's family. The message 1999 sold to me was: Oh kids, don't do bad things or else the underworld police will get you. How the chick got on the ship is already a huge holes in how Hunter association is run.
Killua's portrayal was what made me not watch the 1999 adaptation, because it was so different from the manga. I nearly stopped watching after the first phase of the exam because Killua turned into some broody, emo kid who happens to have bombs with him. Why would he have bombs with him? I don't get this, because (as far as I have watched, which isn't much) this is the only episode where we see him carrying bombs. He is an
assassin. He shouldn't need loud and flashy stuff like bombs because he's supposed to be stealthy. It could work as a distraction and easy escape route, I suppose, but given his skills and Rhythm Echo he shouldn't need such distractions and escape routes.
Then I tried to give it another go, so I watched the Anita filler. I don't know why, but I was amused with the Anita filler even though I was annoyed with Killua's characterizations. Despite that small unfound amusement, I don't like Killua already being made into a good guy. I was genuinely, sincerely surprised with the results of the last phase of the Hunter Exam when I read the manga. If I watched the 1999 adaptation, I don't think I would have been surprised at all, because I already know he's just some troubled, misunderstood kid. Unlike in the manga, where we don't really go in depth with him until the last phase of the exam. The ball game ruined this for me, because not knowing anything about Killua except on the superficial level is vital for the surprise. I seriously wasn't sure if Killua could be trusted at that point in the manga.
Now that I think about it, one thing I would have liked Madhouse to do would be Killua telling Gon during the first phase that he (Killua) and Hisoka are alike. It's not a big thing, and I can do without the change, but that line is what made me unsure if Killua is an okay person in the manga. (Admittedly, the 50-hour stuck-in-a-room filler would have probably dispersed my doubts about Killua too if I watched the 2011 adaptation first. Which is why that one line about him and Hisoka being alike should have been in the anime, because it really did linger in my mind for a few chapters, thus my doubt.)
As for the heart scene, I don't know what's the big deal. Just because he didn't crush it or because it was hidden inside the rag? He killed Jones by ripping his heart out and not by any other matter and that's the main idea.
I think the heart scene was done excellently in the 2011 series, which is why I said it is arguable that it didn't mess up canon. It depends on how someone interprets 'messing up canon' - messing up what actually happened in the manga, or messing up the intent or main idea? I was confused when I first watched the heart scene since I read the manga first, but I really liked it as a substitute. I'd even say I like it better than how it was done in the manga because I always interpreted Killua as more cheeky than badass. Not that Killua isn't badass. I already know he's badass, which is why I tend to look at the other aspects of him as a character.
Him drawing out the moment, dangling the heart in front of the enemy, and then returning the heart after Jones is dead is mocking, yet still cruel and awesome. It's one of the changes that I really like in the 2011 anime.
I never saw that one panel as a big moment for Leorio, considering they all could open the gate after that anyways. It was one panel, nothing really about it that was conveyed as a big moment for Leorio. They all grew stronger at the gate, if they placed so much emphasis on that Leorio part (one panel in the manga), it would not show how much Gon and Kurapika improve in strength as well.
I really did not find it a big deal like others make it out. It did not ruin canon at all, because it showed that they all had grown stronger by the gate. Which afterall is the entire point, not to show how strong Leorio is (a character who appears in less arcs than Hisoka). No offence Leorio fans, but his real big moment is KO'ing Ging.
True, the point was that they all got stronger. But I liked how the manga showed Leorio opening the gate on his own. I suppose what made me like it is because it showed Leorio, as an individual, getting stronger (and not just all of them getting stronger together). It was at that point while I was reading that I wondered what Leorio could do on his own because he mostly got far during the Hunter Exam through other people, even if indirectly (Gon revealed the pigs' weakness in the second phase, allowed all of them to pass Trick Tower in the third, and successfully took Ponzu's tag in the fourth. Killua's actions guaranteed him a license because he killed someone.) We know Leorio is capable, but seeing him open the gate on his own kind of reinforces the idea back to me after seeing him pass the exam like he did. This is more on the interpretation of the scene in the manga than actually clashing with the intent of canon, I suppose?
I admit, I just like seeing Leorio being awesome. Him KO'ing Ging is awesome but that's still a long way from now, so I was really looking forward to seeing him push the gates.
Admittedly, a lot of my beefs with the adaptations (characterizations and changing events) are based on how the manga impressed me as a reader and how I interpreted the manga as I read it for the first time. So with the 2011 adaptation, we can probably say that it stays true to the
intent of the scenes of the manga. It just didn't leave the same
impression with me. But, while I still want a few changes, I can let those slide because experiencing HxH through different media
will leave different impressions because of how the story is presented (like the heart scene, for example).
The problem with the 1999 series, for me, is that it really ruined the characterizations, and this isn't just about how you interpret the characters anymore. They are presenting wholly different characters, really. At least the 2011 series is more faithful. It's not 100% faithful, but it's a better adaptation overall because Madhouse
knows what it's working with. I don't think you really get that feeling when you watch the 1999 series.