Mass effect is one of my favorite series ever! I've played through the trilogy at least half a dozen times now. It's my cozy game I always have a playthrough going in.

Mass effect 1 was incredible for its time, and still pretty good today. The biggest mistake I see people make is not talking to everyone on the ship in between missions (this is true for the whole series); if you don't you'll miss the best part of the game. Also make sure to pick an interesting class, probably something with biotics. Infiltrator and soldier are boring to play compared to sentinel or biotic.

Mass effect 2 was the game that shifted the series from an RPG to a cover shooter. The mechanics were much better, but it removed some of the fun. I remember the first time I played it I was heartbroken the citadel was so much smaller than in the first game. I'd say 2 has the best DLCs of the trilogy (Shadowbroker is unrivaled). I love the structure of 2 as well, but there's definitely a few gotchas where if you do a mission too soon it'll lock you out of finishing important side quests if you want a good ending.

Mass effect 3 is great, the mechanics are more mature than 2, the story and "omg" moments are the best in the series; and (especially with the DLCs) it really fleshes out the backstory of the galaxy and races in a way the first two games didn't. I do wish the team on the ship was a bit bigger, but the citadel dlc is definitely a close second best in the series; and makes up for it imo.

As for the ending of 3 (mild mood spoilers):

So all in all, I think the trilogy is incredible, and everyone should try it. That said you've gotta go in with an idea of how to play it (this is true for all the games, but especially 1), because the games will let you miss a lot of stuff (like crew interactions, important side missions that affect the ending of the game and encounters in later games, etc.). It's definitely a trilogy that's better the second time through bc of it, or just find a good non spoiler guide/video for tips.