Kordras wrote...
I wouldn't say she 'suddenly' falls in love with him. Starting with ME1, 2 years to reflect, and then through the events in ME2 (especially if you manage to keep her from being exiled). Her and Garrus have both been through a LOT with Shepard, so I don't see them shallow. If anything, they make more sense than the Jacob/Thane/Miranda romances, IMO.
Tali's romance seems VERY organic. It flows and it is beautiful when she tells him that she has watched him for so long. That makes it more touching. (If one is to romance Tali, do her the favor of being free and clear of other romances)
Garrus...he's just cool. His is a bit awkward, but that could be due to the rather extreme physiological differences.
Why a Paragon Femshep would EVER go with Thane is beyond reasoning to me. He's a murderer. I think he's cool, I do. I don't like his look, but he does have a certain Je ne sais quoi; that does not mean I think he is a good romance option for a Paragon femshep.
Jacob is all right...but it seems stale to me.
Jack...ick. Too checkered a past for a Paragon Shepard.
Miranda...hussie
Fidelity is another matter. I agree that the LIs from ME1 were given weak roles in ME2 and they were too antagonistic to Shepard, but that does not mean Shepard should 'cheat' unless the relationship is definitively over.