I like to think of Mordin as a very ME1-esque character. A lot of the characters in ME1 are very troubled, sometimes they have interesting shades of grey or flaws. Liara is a naive princess who despite that tries to handle things in a friendly manner which isn't always the best decision, Ashley is distrustful of aliens but at the same is pretty open, Wrex helps contribute to his people's suffering by actively being a merc and even acknowledges this, Garrus uses renegade style police work in light of being an upstanding cop. That's what made most of the characters in the first game interesting. Tali and Kaidan are exceptions but I could make the case that kaidan is one too, it's just that he's boring as all fuck about it.
Likewise, I find Jack, Mordin and Thane to be in the same category in ME2: really flawed and interesting characters who do questionable acts who try their best despite their intentions.
I like how ME2 characterized Liara.
I hated how they handled Ashley/Kaidan in ME2.