Nothing like Fallout.
ME is pretty linear, while Fallout isn't.
ME's combat is superficially similar to Fallout's real time combat, but that's like saying Duke Nukem and Half Life 2 are similar just because they're both FPS.
Item and inventory systems are completely non-existent in ME as they've streamlined it, unlike Fallout.
ME has a moral system akin to the other Bioware games like KOTOR, Jade Empire and whatnot. Don't think Fallout has that aside from their karma system which works pretty differently.
One is a high sci fi setting space oddessy. Fallout is a post apocalyptic story. I guess you could claim they're both Sci Fi, but see above comparison on FPS.
Both decent games though. No reason not to get both, unless there's an aspect in one that you really can't stand.
For me I like games like Morrowind/Oblivion and Fallout, but don't have the time and committment to do that much free exploring these days, and prefer something with an endgame clearly defined like ME. Some friends of mine find ME too linear, or are not taken by the far future setting.
But if you have no idea either way, I'd suggest ME is definitely a good game worth a pickup.