But HL2's editor is very limiting compared to the point editing capabilities of a full 3D modeling package, which Metroid Prime can take advantage of, but HL2 can't. HL2 levels are built by combining simple 3D primitives together (cubes, spheres, cones, simple stairs). More complex objects (prefabs) can be impoted from a 3d program, but they are just add-ons, placed on top of the environment instead of being a part of it.
Metroid Prime environments are created in a full 3D modeling package, giving the artist greater design freedom.
I would never, ever, want to work with an editor that forced me to use a full 3D modeling package to make an entire level. The reason things are built by combining 3D primitives is because this is easier to do. It is possible within the Hammer editor to edit vertices and pretty much do whatever you want with a block (save making it a concave shape) and as you said, you can import anything that needs to be imported from a 3d program. Having worked with both editors (Hammer, Radiant, UnrealEd) and 3DMax, I dont think that having an editor detriments the building of a level at all.
I think what you are knocking HL2 for (and go ahead, its kinda valid) is its artistic direction. Some games have excellent artists behind them that are given creative freedom, others dont. HL2 wanted to make Eastern European hell, I think they did it. Metroid Prime (and I've only played a little of it) was creating the interior of a ship and I wasnt really paying attention to my surroundings, so Im not gonna comment on their artistic direction.
I'll bet that within the HL2 editor, it is possible to recreate a metroid prime level. You would need to import many many textures, and many models, but its probably possible.
edit: misplaced quote markerThis comment was edited on Sep 22, 10:14.