It speaks of the skill of the mangaka to convey the characters' emotions and affect the reader. I found myself sympathizing and empathizing with the characters many times and eventually rooting for Midori and Tokio's happiness (and Wakatsuki's, he's such a wonderful character, how could I not!). There are dramatic moments, but as long as the characters have realistic reactions it works to the manga's advantage. There is a love triangle but it's handled extremely well - and by that I mean that the mangaka spends time DEVELOPING it for maximum effect.
The main thing I love about Eden no Hana is its characters; they all seem very human to me. The three main characters, in particular, are quite mature, which was a pleasant surprise since most shoujo characters tend to... not be so mature.
Midori - She's a refreshing protagonist. Her isolated behavior makes perfect sense after what she's been through, and her emotional barriers present a challenge to others (and to herself). It's a pleasure to see how she continues to grow and opens up to relationships with Tokio and Wakatsuki's help.
Tokio - His struggles to understand Midori and to define his position as her brother is admirable, amusing, and heartbreaking. I just really enjoy his warm personality and his attempts to chip away at Midori's walls.
Wakatsuki - I like how the 'third-wheel' character has an actual personality. He's evidently one of the smartest in his class, but the reader isn't hit over the head with it. I see in shoujo that the potential male love-interests have so-called defining qualities, mostly superficial - smart, handsome, etc. But Wakatsuki is as multidimensional as Tokio and Midori.
I'm also adding the 'Uncle' gardener who takes care of the school's roses. He's a minor character but he contributes to the story, oftentimes acting as a neutral confidante of Midori. I like how the mangaka doesn't overpopulate the manga with extraneous characters. The 'antagonistic' characters, the foster brother and the classmates are quite... ah, terrible people. I wonder if the classmates, at least, will show some redeemable qualities but at this point in the manga it looks like they're about to do something irreparably damaging to the heroine. :/
EDIT: Halfway through and... when a manga has be thinking, 'OH, HEART, BE STILL~!" then I know it's good. 🙂
EDIT: Done, except I struggled my way through the last few chapters since I have the raw and there aren't any scans (darn!). My god. This was fantastic. I even started to feel for the crazy father in the end. Sobbing forever. The ending was nice but I wish there was more. After all the sadness and angst going on I felt entitled to more happiness. Oh, and the watch and rose symbolism was lovely and well thought-out. This was beautiful and I upped my previous rating. Sigh, this manga leaves a void in me...need to find another manga now.