Rantings of a Mad Woman. (Help me!!)

So looking back on my ratings from this year I've noticed several cases where I rated something higher than I actually felt about it. For instance if I didn't totally hate it they seem to have gotten 3 stars. I was new to the whole book blogging and rating game and I don't think I've done a great job of it. I think I want to go back and adjust it better but overall I don't think the choosing a rating on a whim is working for me. So I need help choosing a better system, maybe one with criteria and such, I'm not sure. What ways do you follow or have you heard of? I'm trying to find a new one but if I do do I need to go back through and adjust all my old ratings to reflect the new system?

 

HELP ME! Any idea you have is better than my lack of ideas.