I played through the entire first two games, but couldn't play 3 because it made me barf buckets' worth out of the pure stupidity. So, prequel-time.
Sequels: God no. Prequels: Kaching (and for actual good reasons, Bioware *Cough* ME3 *Cough*). There's quite alot of good lore that the prequels could use, definetely.
Ofcourse, going *completely* back's an option, too. What about a Dragon Age: Origins-style thing. You can choose your Race, Gender, chosen skills, main skills, ect, but keep the Mass Effect dialouge and combat. Mix in some good writing,(which I know Bioware now urinates) an open-ended plot, fix some of the combat-issues, and make up a new backstories with lore to connect it with its chronological sequels. There, Bioware, you have a game, one that will be much better than ME3. I expect 15% of the profit.