The good parts of Mass Effect 2 were great. Voice acting is fantastic. Combat was streamlined from Mass Effect 1 making it excellent. The RPG part was also streamlined, eliminating a lot of the busywork from ME1 without losing the customizability.
What I expect from the Mass Effect series is an adult science fiction game. Why then is Commander Shepard limited to such puritanical sexual relationships? I want to play my Commander Shepard like Captain Kirk, sleeping with every available crew member or mission encountered alien that I can! Instead, what I get in Mass Effect is a very linear and monogamous relationship system only on ship were all the potential romantic participants are apparently talking to each other. It's just like High School. Downloadable character Kasumi's only ship function appears to be relationship gossip. The main characters all never appear to leave their assigned ship rooms, yet everyone knows everybody's business! Other than Kelly, all other characters are prudes. If I had to hear Jacob Taylor say "Let's not push it, we got a good thing going here Shepard" one more time, I would've thrown my controller at the Xbox. The system is to on rails.
What I would do if I were designing the game is to leave all sexual relationship options available at all times, just make those decisions tie to paragon/renegade points. If Shepard has already started sleeping with a character, and then tried to pick up another lover, that choice could feed into the complexity of your character more completely. Play with the highest honor on the battlefield, but be a total dog with your crew, or vice versa. I even have a problem assigning renegade points to a Shepard that sleeps around, but within the design of the game doing that would be the cleanest "fix". Also each character could have different relationship needs to achieve their highest morale. In ME2, all potential romantic characters appear to have the same end need, a monogamous relationship with Shepard. Again, Kelly excepted, but even she won't continue or start a relationship with Shepard if Shepard has already started something with another character, and she's the "slut" of the ship.
I look forward to the day when I can play as a character in a game that was as open as Captain Kirk over 40 years ago.