I actually disagree. The rest of the image isn't anti-aliased either.
As far as the halo goes... I dunno. Not required to have I think unless in the same level it was done also.
I think the new tree looks great, as does the new grass. I prefer your original sun though. In real life when you can see the sun clearly, it turns orange at the edges, but the sky isn't blue at those times.
I'll try to make it as you suggest, but I think you were supposed to have an attachment there, or did I miss something?