My top 3 would be...
1. The emotion of the game.
2. Characters
3. Hybrid ME1/ME2 Gameplay
Overall the BEST game series I have ever played. The ending was... yeah. But that's OK cause the rest of the series makes up for it. 10/10!
1. The emotion of the game.
Seriously. I cared more about the characters in this game that I think I have in any other game. Mordin sacrificing himself and singing his song during the fire/explosion and space cancer Thane beating the crap out of Kaie Leng come to mind.
The characters in the game were also super good. I mean chilling with Garrus on the roof or trying to seduce Joker were just so funny and cool. It really felt like the characters were real.
I feel like the gameplay was the best in this game and provided a good balance between ME1 and ME2. You got the easy to upgrade gun system with mods back but you didn't have to swap all your gear every 12 seconds cause you looted a box.
Overall the BEST game series I have ever played. The ending was... yeah. But that's OK cause the rest of the series makes up for it. 10/10!