My first impressions of them: I had pretty much given up on pokemon by the time DP came around and I'm not too sure what my first Shinji episode was. In fact, the first time I remember hearing about him was in one of Dogasu's episode comparisons. Back then I had a lot of respect for Dogasu but when he started saying that in DP, there's a character that is nasty, powerful and three dimensional, I couldn't believe it and had to check it out.
What I think of their design: One of my all time favorites, just by how well it fits him. I love the colours the hair the everything about his design and I really like how there's symbolism but it's played subtly if at all thereby creating a feel that doesn't use the cliches that a lot of children's media and thereby gives him a mature feel.
What I think of their role in the story: As a element in Satoshi's story he was excellent, if anything too good: often making me wonder if Shinji would make a good spin off show rather than thinking about what's actually shown (though I think about that plenty too). That said, inspiration is a good thing and being a strong character whilst doing that is exciting.
What I think of their interactions with other characters: There are two that instantly come to mind for me: Reiji and Satoshi. Satoshi has a great rivalry with Shinij and one that has it so that, despite Shinji not being a mayor character, he still pushes the whole feel of DP with many characters reflecting him and expanding on him, both literally and in a meta sense. Shinji's interaction provide more than just critique fuel though: he's a dork towards Satoshi (and Reiji) and we can laugh at him and admire him. Whilst he pushes DP's theme, analyzing him to the level that I have, simply isn't needed to enjoy him and a lot of that is due to his interactions with all the characters: ignoring Hikari until he can talk about Satoshi, seemingly only being able to talk battle stuff, being hated by TR. Basically his interactions with characters are a large part of why he's enjoyable. I just wish we'd have been able to see more.
My favorite aspect of the character overall: Okay, this is hard to choose. I think I'll have to say his relationship with Reiji which I have several ideas about to say the least.
What could have been improved or changed with regards to the character: I think that it would have been better had Shinji been given more screen time with Reiji and his writing not been tied quite to Hikozaru so much.
My number one wish for this character: I'd like a spin off show, please.