It's funny--in a house with three tvs, three 360s, and three copies of Fallout 3 (including my own), all I can put serious time into is this. I played through the first seven regions of story mode on my roommate's PS3 and spent enough time with the level editor to be able to quickly construct rocket-cars, tanks, and other vehicles. My favorite level is possibly Frida Destroys Everything With Her Skulldozer.
Anyway, I'm at my girlfriend's place today with my own PS3, and it's nice to see that the vast majority of the tutorials are easily skippable. The only mandatory building tutorial you can't skip if you want to use the associated icon is the one on making creatures. Still haven't quite gotten the hang of it, since most of the enemies I'm building seem indestructible, no matter how many times I check the "vulnerable" checkbox and verify that yes, I used the "unprotected" brain-type. Jump up on 'em, shoot electric bullets at 'em--nope, they keep plodding along as usual. Weird.
I would love to see a tutorial on making level-sized objects out of material that doesn't quickly get "too complex to add any more material to". I think the trick may be to create smaller building parts that you stamp down a bunch of copies of and then glue them together.