It’s been ages since I’ve been to CA Universal. Based on the research I’ve done, I know that it’s a single park vice two parks and does not have as many attractions. What it DOES have is the back lot tour, which I remember being quite good. Others will have to provide more specific guidance.
As for the weather, I can comment with some authority (having lived in Southern CA for 6 years) that rain is MUCH less of a factor and in general, the weather is more moderate year-round.