Well first game I've played was Mass Effect: Andromeda, for the PS4, and it was a good friend of mine that got me to buy it and play it. Enjoyed what Andromeda had to offer and my friend suggested that I go ahead and buy the original trilogy. I fell in love the story setting, from the original trilogy, and the companions that I've encountered from ME:1, through fighting the Collectors in ME:2 and transcending to the final battles for the Milky Way Galaxy in ME:3.
I think ME:2 would be my favorite from the original trilogy because of the Suicide Mission and the DLC of the Shadow Broker. If you didn't take the necessary precautions throughout the game your actions during the final rundown in the Collector Base can have a serious effect on your crew and Commander Shepard. As for the DLC of the Shadow Broker I really enjoyed teaming up again with Liara T'soni. I really enjoyed the entirety of the mission. From the sky car chase to navigating the Shadow Broker's ship and fighting the Shadow Broker.
For some of the most memorable moments I will have to lean toward ME:3 with the DLC Citadel where Shepards' interaction with his past and present crew mates during the party scenes. It did give me quite a few laughs.
As far as favorite character(s) I would have to say Liara T'soni just because she reminds me of myself. When you first meet her in ME:1 you can sense she feels a bit out of place when she joins Shepard's crew, reserved, informative, and mature. Later in ME:2 and ME:3 you see her being more opened, relaxed and independent in a way. Another would be Garrus Vakarian a renegade Turian that pushes himself above and beyond he has that appeal of 'more than just a sidekick' type of attitude. Out of all the romances and conversation scenes on my (F) Shepard I prefer the interactions with Garrus. He's a friend that will stick with you to very end.
The only problem of the ending the trilogy would be the final choices Shepard has to make in the final scenes of ME:3. It was very disheartening that the journey you created for Shepard really doesn't have a so called "happy ending" it comes to a tragic ending of sacrifice. It left me discontent and sadden which leads me to worry about what may come to my Ryder character in ME: Andromeda. Will they too succumb to a similar fate? I guess time will only tell.
