So I don't consider myself much a fan of romance novels, but I do enjoy character development a lot. The EH series has Char Dev in spades. I found it really easy to get invested in the characters (even if I wanted to slap them upside the head for being stubborn), and the overall plot arcs in the novels have felt pretty consistent. 4/5 stars, worth reading all three in a row.
Experimental Hearts is a great series for those who enjoy in-depth character development. The entire series takes place in a vividly described world, blending the modern world and a world full of magic, power and dragons. The characters are sassy and full of attitude, too.