As for romances, I rarely bother with trying to romance other than one love interest (usually Kaidan for femshep, though one game save, I romanced Thane.). This is primarily because some of the most awkward dialog is associated with the other romances that I start giggling helplessly and can't follow through. I was able to rekindle the femshep relationship with Kaidan, which was a nice bit of closure, because it felt bad in ME2 when he sort of rejects you/no longer trusts you.
I play ME like I play FF and Persona -- i.e. collect/experience as much of the story/characters/equipment/tokens as possible. If the over-earnest character interaction and story give me an unintentional laugh or two along the way (and/or, on the rare occasion, even manage to make me care), all the better.

I leave "my" playthrough for last.
I do think the Liara/Shephard relationship -- what I've seen of it so far, anyway -- is well done. One interaction in particular even managed to make my throat lumpy!
Hmm.
Spoiler I was pretty much 100% loyal to Liara from ME1 to the end, in my "true" playthrough. I was able to get a scene in ME3 with Traynor and a beginning with Allers, but I reloaded those saves to do it "right", so I don't know what Liara says about it. Given that there were jealousy/gotta-choose-one dialogues in ME1 (no idea about ME2), I'd guess that you can't just romance everyone freely in ME3, and there would have been consequences for jumping in the shower with Traynor.
I was hoping they'd changed the relationship dynamics for 3. Seeing as the status quo of the entire universe is unravelling, you'd think a lot more people would be up for one night stands. Don't know if I'll want to replay this multiple times just to experience the other characters, though. I'm doing three playthroughs -- one standard game, one game with DLC and saves, and a final, "proper" playthrough. If I don't cover all the relationships by then, I'll probably just watch the remainder on youtube.