Excellent first fontstruction! Some pointers:

- The Q is missing a tail

- The bottom half of 7 and ? could be closer to the middle

- The exclamation mark looks a bit too tall

- I would lower the crossbar on 4, make the dots of the umlauts a bit closer together, and remove the stub at the bottom of æ.

Cheers!

Beautiful polygonal letters. They look decent at large sizes too. Not smooth, perhaps, but rugged. There is virtue in robustness, plenty. A have a few suggestion to improve Onion:

Capital M,W, and to a lesser degree the N, does not fit the overall style of your font. The lower case letters show no such problem. 

I would make the ascender of the "t" a bit shorter.

Diacritical marks: the grave and acute on è, é should be different from punctuation marks.

The § usually goes down to descender territory.

Font name: there is already a font called Onion, published in 2007.

http://www.fonts101.com/fonts/view/Uncategorized/42519/Onion

Ther is another one called Mrs Onion: 

http://www.myfonts.com/fonts/hipopotam/mrs-onion/

Hint: Mr Onion is not yet taken.

The spacing is generally good, the text generated is pleasant to read.

A few kerning issues remain unresolved, but Fontstruc does not support kerning (at present).

You said, it was your first fontstruction, and only used original bricks? Amazing work. Congratulations. 10/10

You made a useful sans serif text font, it looks very tidy.

I have one observation: the "j" in my sample text looked detached in the word. I would move it half the width of "j" or more towards the blue line until looks like it belongs inside the word.

@macurious: A slight misunderstanding. A meant the § stretches across from ascender to descender, just like in this sample: N § J. If you are not sure about something, the best way to check classic fonts already in use.

The shorter "t" is a nice touch commonly used to improve legibility. It is discretionary, of course, but it looks better in the frequent word "the".

It's tricky to find a good font name. Since tens of thousands of fonts are in circulation, the best words are already taken. Some people circumvent this problem by adding initials to the font name, e.g. FS Spoon (FS for Fontstruct). Before final decision, just make a quick Google search.

Yes, it looks better :) Yes the j links into g,j,q and y, it doesn't look 'bad' but makes the design different from other fonts, yours has alot of personality. Your first font, wow, is really good, well done!

Nice angular design. I have a few suggestions:

—I would raise the tilde, greater than, and less than signs to the hyphen height, i.e., center them on the plus/minus.

—I would make the circumflex a bit wider.

—I would make the down angle of the sharp s like the v.