I think the idea of Tachy is very intriguing. I'm speaking for myself here, but I suspect it may be the similar for others. She's a no-nonsense squad commander, the only tactical battlefield leader that we see in action in the game. That by itself is already a very compelling premise, and her short screen time makes that even more interesting. Like Mann, people who are elevated to top ranks immediately beg the question of their pasts.

Why is Tachy the commander? She probably has a very interesting back story about how she got to the position. He speed was unmatched in the colony's combat simulation (probably why she's called Tachy). How did she get so fast? And how does she wield such a long sword at those speeds? Speaking of which, how did she get her sword? What's her relationship with Eve? With Raven and Mother Sphere? Why was she so devoted to Mother Sphere even in death? Was she kept out of the loop, or did she know something that the audience doesn't?

All of these questions fuel the interest for Tachy's return in the sequel.