There's three different model "families" out there for the BioWare Aurora-type games [1].
There's the NWN family, with NWN, KotOR/KotOR2, Jade Empire and The Witcher. They each are obviously descendants of each other, built using similar concepts and structures. However, NWN's animations are mostly node based (the geometry stays the same, and only the position and orientation changes [2]), while the later games use bone/skin animations (the vertices of the individual meshes change too, following one or several nodes (bones) with certain weights).
KotOR and KotOR2 models are nearly identical, with only some minor differences. Jade Empire is similar to KotOR, but differs more. Similarily, The Witcher's models extends on NWN's, adding new features like LOD nodes and shader materials.
All of these games still have readers for the ASCII versions in their binaries, too [3]. Very helpful for figuring the format out '>.
The second family is NWN2. It's structured completely different, and reads more like an IFF file [4], with the 4-byte packet ID and size field. No animations specified there, as NWN2 uses Granny and FaceFX for body and facial animations, respectively.
The third family is the format used in Dragon Age: Origins and Dragon Age II. GFF4/XML-based, and again structured very differently from the other families. The DAO and DA2 formats themselves are very similar to each other, with the main difference being that the latter moved to using GFF4 instead of XML (for performance reasons, I guess) for materials.
As for Mass Effect, I'd assume they use formats more native to Unreal Engine 3. But I have no clue.
[1] Four, if you count the NSBMD format that's used in Sonic Chronicles. That's a native Nintendo DS format, though, also used in other non-BioWare NDS games
[2] Meshes can also be completely swapped, and the dangly/jiggly meshes do change vertex positions
[3] The NWN ASCII MDL format seems to have been based on the Wavefront OBJ format, it seems?
[4] In fact, I wouldn't be surprised if it was based on some other, existing model format. If anybody knows more about this, I'd be interested