Overall 22 hours. 100% pickup, all endings unlocked.
Not a very long game. Zelda took me 50 (as i recall). lol.
The final boss battle wasn't that hard actually. It could have been a bit more difficult but after MP2 I'm sure retro wanted to make something a bit easier. You basically just lock on dark Samus and fire away. X-ray when she splits. The AU afterwards was a bit harder. You have to get those tentacles quick. Afterward, as long as you keep from getting over loaded, the final bosses are easy.
Retro has shown us what a First person shoot on the wii can be like ... now lets have the control interface of MP3 and a online multi-player and OMG you have a pretty damn good halo 3 fighter.