She's compassionate- and kind- and often tries to cheer people up when they are feeling down, this shows a lot in the series, she even put lots of effort into putting on a circus for Ash, when he was feeling down after his defeat to Paul, and she also helped Maylene get her confidence as a gym leader back. She's also determined to do her best at almost anything she tries- and she teaches you to never give up!
Everything I like about her would warrant my own thread discussing the topic, but for now i'll just list my personal favorite highlights. 1.) the team work between her and Ash. No other of Ash's traveling companions went to the lengths she did to support him with a few being teaching him the spin dodge he employed against Roark the ice aqua jet she came up with but Ash perfected with Buizel, giving Ash the inspiration for the counter shield, etc. 2.) She's the most well developed of his female companions, being overly confident despite being new, to her confidence getting damaged due to a losing streak, to going on to be the runner up in the grand festival, she managed to overcome her short comings with her relentless determination to achieve her dreams, improving herself as a result. 3.) Her synergy with Ash appears to me to be the most natural out of the girls he has traveled with. her personality is pretty similar to ash's all around, even reminding me of how Ash used to be in the first series (Though shes' smarter and matured more quickly than Ash did because male anime protagonist). They both are kind, willing to help any people or pokemon they come across who need it, they are both fun-loving and optimistic and they both share the same love of their pokemon. These are my top 3 reasons I love Dawn as a character. And that was longer than I wanted it to be. I'm so sorry lol XD.