I would not call it interesting. It's schizophrenic. Let's ignore for a moment that Liara is constantly thrown in your face (as much as her DLC in ME2 is fun, having good boss fights and a good setup) it's almost embarrassing how the game pleads and cries to the player to let Liara shine as the perfect blue-skinned waifu.
But her character between ME1 and ME2 is shredded and rewritten entirely. I'd dare to say Liara in ME1 and Liara in ME2 are different characters altogether. Garrus keeps his vigilante and hardass motif, Tali keeps her dutiful but curious character. Liara in ME1 is a naive researcher, in ME2 she's a completely hardass spymaster that rivals the Shadow Broker.... just because. You can almost feel the writer of 2 trying to half-ass a justification by "uhhhh archeology is tote similar to information brokering uhhh it's- uh, the same".
ME2 is tonally quite different from ME1, but Liara is one of the most clear examples. I'm quite curious about her going in ME3, maybe she gets another rewrite.
I think Liara's character shift makes sense as it's presented, but you're right that it's a hell of a tone shift and that the writers give Liara far more attention than the other characters. The problem is that most players went with their Blueberry Waifu and there was a lot of expected fanservice around her as a result. Had more people romanced Ashley/Kaiden, they probably would have gotten a bigger role in ME2. It doesn't help that Liara, as you say, throws herself at the player. I would agree 100% that the other characters deserved more meat for their romance arcs.
Also, as someone who was in academia once upon a time and now does stuff related to the information business... they're a lot more related than you might think. Research skills are highly valuable and very transferable. That said, I do understand your point and I don't mean to say it's invalid or even wrong. I never saw Liara's jump as that strange but, after reading what you wrote, I can definitely see how others could see it as making Liara more badass for the sake of it.
Overall, ME2 was more grimdark than it needed to be, but it was 2010. The atmosphere and tone of ME2 does not hold up nearly as well in 2025 as ME1. Liara is much more consistent between ME2 and ME3 than between ME1 and ME2.
Agreeable. But Morinth is merely an example: ME2's writing can only describe, not execute. Morinth's speech is essentially "I LIKE DRUGS I LIKE DANCING I LIKE RICH WOMEN NOW OBEY ME". I'm not even exaggerating much, it's that blunt. I do not demand Avellone writing Planescape romances, but at least basic attempts at writing memorable or atmospheric dialogue.
For your question, after ME1/ME2.... Zaeed is a fun carbon copy of Canderous. Krogans may be all repetitive klingon lizards, but both Wrex and Grunt are amusing squaddies.
I don't agree. Morinth's speech is really "I'm being hunted down for choosing freedom over a millennia of cloistered life." Some people might resonate with that. I didn't find Morinth very interesting, or seductive, or even compelling, but I do see what the writers were trying to do with what is essentially a side mission that should take you 30 minutes to complete. The writers could have done a lot more, but remember that EA bought out BioWare and wanted results. I played ME2 at release and hooey did it feel rushed compared to ME1.
Zaeed definitely hits the "reliable sci-fi bounty hunter" trope that people, like me, enjoy. I thought that Zaeed was different enough from Canderous Ordo but, then again, I have not played KOTOR in a very long time. Wrex and Grunt are interesting for their juxtaposition. Wrex is a very old krogan who has seen it all, while Grunt is literally a teenager. In general, I found Wrex to be a strong and well-done character, but others disagree.