Since you asked for a critique I hope you don't mind that I changed your photo to a grayscale so you can see the values (or rather lack thereof). If any kind of realism is your objective try and be aware of your values. Do you use a value scale when composing your image? If not, value scales are quite helpful. I notice the rather large areas of similar light mids in the sky and grass, which composes most of the painting. Just my $0.02. If your objective was met with the values you've chosen then.... never mind
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Susan I don't want to hijack Neil's thread (sorry Neil) but I like how Stan Miller explains value and color. It's watercolor but the principles are the same for oil.
This is one of his exercises that is pretty good, it is about the relationship between value and color. (colorists don't generally like this video but it is a value and color lesson so he's trying to explain that for realism value tends to be emphasized over color if you want your painting to mimic life).
Thanks everybody. Agreed about value. Hadn't even crossed my mind. Thanks. And yes it is on gessoed paper. My mistake. I'll concentrate more on value from now on. Very cool realization for me actually.