Kai Leng looks like he jerks off to pictures of Adam Jensen.
In ME3 it follows Commander Shepard after Reapers are now realized as a real threat. In no time Reapers attack earth where Shepard must proceed to acquire forces to help defend earth from said Reapers.
The combat is really stepped up in ME3 where some new things are added such as the blade melee attack, using Kinect to order teammates works surprisingly well, everything just seems more accessible.
ME has always been good at making you feel like you are a part of something bigger with the amazing atmosphere and story; which is a stand out in the finale.
The only problems I had with the game was the awful quest managing system, smaller range of characters to pick from the last ME game and that really bad ending. Touching on that ending I will say that it pretty much kills any need to replay the ME series. Everything about it makes you feel like it everything was for nothing.
Is it better than Mass Effect 2? No.
Edit: I forgot about Kai Leng, I couldn't even take his character model seriously. Don't even get me started on the "fight" on Thessia.