Here are my opinions and hopefully you won't be offended about them!
This is great, but it looks little bit plastic to me. no, dimensions - a bit flat.. It's too pale and it's little bit hard to read text "The Friendliest Forum..." Pale blue and green is not so good combination - probably.. On the left, plants could have some colours too.
Nice fishes, also neat banner - but it's almost impossible to read text. You need to concentrate when reading it. If you just look over it quickly, you cannot read text. Also background is wrong. (Well, William wants to use blue background.)
This is awesome! Very good! Nice colours, easy to read. But no fish? Well, do we really need to have some fish(es) in banner? Probably no...
I think this is absolutely awful
(Sorry!) Idea is very good, but it looks quite messy. Probably you tried to make it in that way, but this is not as good as others.
It's nice, but there is too much noise. (wrong bg too)
It's too ordinary
Too much noise too, when comparing it with the forum itself. (wrong bg too)
Like you already said it - it's too dark.
Welcome back to to 70's! It's retro.
Nice, but it's a little bit fluidish B) Bit a gel-like... It's also hard to read text. (wrong bg)