The universe of Mass effect was founded on curves. Curves in space, curves on ships... hell, even their weapons had curves!!
Mass Effect 2 either forgot this or there was some fundamental shift to a parallel universe where people can be magically resurrected after de-.... oh, wait. Does that explain the story of ME2? Anyway, the shape du jour in ME2 is the rhombohedral, specifically parallelograms. The world has it, Cerberus' insignia has it the ships have it... hell, even all the new weapons have it!
Mass Effect 3? A little too early to tell... but i'm going to go for hexagons.
ME1: Save the universe at the cost you see fit. It's a classic pulp sci-fi endeavour complete with inspirational music and varied environments that are fantastical in nature. A bit like an entire series of Stargate or Star Trek rolled into one game.
ME2: Guns of the magnificent seven. The story of 2 is very simplified and actually doesn't make much sense if you let yourself stop and think about it for even a minute. The environments are more bland and similar with fewer types of area to visit... the art style is more utilitarian and less fantastical. The only mission that felt like Star Trek was for Jacob's loyalty, the rest? Bleh, Gears of War eat your heart out.
ME3: We'll see but i'm pretty sure it's Battle beyond the stars with smatterings of both the previous two games.
I'm sure there are more things that you can think of that trend to the untrendable for Mass Effect and its universe. Let me know via the comments or our email address: the.easiestbutton at gmail.com.