Play all three, and go for a full completion.
ME1 has atrocious teammate AI (at least the PS3 port, I don't remember how it was on PC), annoying inventory management and is generally clunky in terms of gameplay, but it offers the best in exploration - the galaxy really feels huge.
ME2 and ME3 are much more streamlined, quests are replaced with missions, where you go to the designated area, go through the mission and never come back again. They're much more corridor-ey and sacrifice the rough-around-the-edges RPG focus of ME1 for RPG elements and play much more like a shooter. They also add an "interrupt" command to conversations and a lot of those are really worth it.
Play male, play female, play full paragon and full renegade, think up a character and roleplay them. Import saves and remember - there are no *bad* decisions. The consequences play out later in the trilogy, but you're never really punished for making the "wrong" choice. So do what you feel your Shepard would do, and enjoy the show.
ME3's ending is indeed pretty bad, but for me it felt more tedious than "OMG story betrayal!".
The games also play around with some scifi tropes, so a fan of the genre might get a kick out of it.
chiefohara said:
Tricia helfer is the superior voice actor, not that mark meer is bad, its just a great story from a female perspective as well.
Sir Thomas Sean Connery said:
Also, you should seriously consider going FemShep. Helfer is a far superior voice actress
FemShep's VA is widely considered to be better than MaleShep's. But it's Jennifer Hale, not Tricia Helfer.