A couple of the shots are really good mate but you need a couple more higher quality shots for a higher quality calendar. Now it feels like it's a collection from 5-6 different photographers.

I'd say yes if you can use better photos.

Jan - NO, too bad light and contrast. Very low quality

Feb - NO, too dark and nothing that's interesting enough.

Mar - YES, IF!, you change it into B&W since that'd work much better. It's very low saturated now and converted to B&W and would increase it's levels and give it more contrast.

Apr - YES/NO, fairly ok shot but the composition is too easy and plain, needs more attidude. Maybe another crop can save it?

May - YES, this works, it's a decent shot and interesting enough to be able to stand alone as a photo. If possible, to NOT have the facing heart in the middle would strengthen the composition.

Jun - NO, too ordinary and can't be saved through the flip.

Jul - YES/NO, maybe too dull in light/composition. Maybe with less sky and more foreground this would get better lines?

Aug - YES, a classic sky/water shot that always works, might be better in B&W due to the contrast ratio the shot has.

Sep - YES, rays always works when the compositions are decent. If possible, structure on the sky would be great, still works without.

Oct - NO, not much right here anywhere.

Nov - NO, could've been cool if you'd composed it less flat and lifeless, doesn't cut it alone due to the composition I think.

Dec - YES, best image of the whole calendar, hands down. Nice dynamic range and contrast. Nice tones and composition, it's interesting. Nice job!

Hard critique? Yes but it's a filthy business and I know you can handle it!

Later Tobi, keep it up!

/rob

Really like the calender, especially November and my month February.

Das ist SEHR yes!

I <3 September

I can't see anything at the link

Don't like January or May. Just my opinion though...
The rest are quite good.