My first ever map! Please review!

Ok, so my first ever map is pretty much finished. I've spent only about a day with hammer, so i'm a noob~ Theres a few bugs, and i haven't got a clue how to make the game know you lose your cube and give you a new one (So just try not to lose it, theres a hidden one in a /special/ place if you do) and theres something wrong with a door, but it still works. and theres a door that likes to be different.

It's not hard, but hopefully it's not /too/ easy either. It was sorta just a first go from me, with a few simple puzzle elements and fast aiming skills. nothing compared to some maps i've seen here
And i wanted the ending to be different to it is, but i stil need to learn more about hammer to get it to work, sorry.

http://img228.imageshack.us/img228/2387/por1.png

http://img831.imageshack.us/img831/3116/por2.png

http://img26.imageshack.us/img26/1264/por3c.png

http://img534.imageshack.us/img534/1690/por4.png

Video!

http://www.youtube.com/watch?v=nrQ-TLiwfyQ (Is of a previous version)

And download:

http://www.mediafire.com/file/250yb6.../firstmap1.bsp

Please give it ago, tell me what you think, any critism is welcome (Apart from telling me obvious bugs i don't know how to fix yet )