I'm a die hard Thane romancer, but I'm currently playing through with a Garrus romance for the first time and...I totally get the hype now.
That said, I do love that you pointed out how truly alien Thane is compared to the rest. He's the one romance option who doesn't just look like an alien, but his behavior is alien. Drell have behaviors and beliefs that are so foreign that they can be difficult for humans to comprehend. The way they view the body as separate from the person in a very literal sense is something I had to work to wrap my head around, and the burden of perfect memory is hard to imagine. It's great worldbuilding and adds dimension to universe where, up until then, most species on your team acted more or less like humans with a different coat of paint or body type.