In Final Fantasy VII, there are two art styles at work. On the overworld, everyone is blocky, cute and deformed, but jump into a battle -- or look at the game's promo art -- and suddenly everyone's adult-sized and finely-detailed.
3D artist Nix has taken the same approach and applied it to Mass Effect. Not intentionally, mind you, but just like Destructoid point out, it's the first thing you think of when you see it.
Or maybe it's the second, after Final Fantasy Tactics.
Wrex, Thane and Liara are adorable. Hell, even the Reaper is worth a cuddle.