I lived in the Sac area (Citrus Heights, worked in Roseville) for 6 years before moving back to the midwest.
Yes, cost of living tends to be high. Expect your car insurance to be high (mine dropped by half when I moved to Chicago area), gas prices are high. Income tax is high, at least compared to what I pay now. When I moved to Chicago, my overall cost of living went down a little, but the big categories shifted around too.
Property taxes are 1% of assessed value for the county plus whatever else is thrown in - school/utility debt, special districts funding, sewer/trash, etc. Assessed value is the purchase price + the lessor of 2% or cost of living index change. So if the COL index goes down, then your assessed value actually goes down too. That happened in 2012 I think (can't remember the exact year). If you do an addition, major work, etc that can trigger a reassessment as well.
Non-financial considerations. Allergies tend to be a problem in Sac. Even if you don't have them, a lot of people develop them after a few years.
Climate in Sac (not the foothills) is different than the midwest. It doesn't rain in the summer, and there was always a day or so of 115+ F. It's a dry heat, but at that point it's a blast furnace anyway. Winters are 40-50s generally. You don't really get spring and fall. It's basically 2.5 seasons. For me, that messed with my head after a while. Once you get into the foothills, the climate changes quite a bit. California as a whole has just about every possible environment. If you do move there, make it a point to do some travel to the middle of nowhere that is much of the state. Some beautiful places (after the 5 hour drive to get there).
Culture - is different. Some of it's obvious, but a lot is subtle. I'm blunt, and people didn't like me much because I'm not PC enough. San Fran is just plain nuts. Go north and you get in to very rural areas that tend to be very conservative. SoCal tends to be very liberal, and since they have more people you're stuck with it.
Politics - living in California is the reason I don't follow politics anymore. It can be maddening. The state is also having financial problems, much of it caused by being stupid (told you I'm blunt).
Something that I was told many times: if you move to California, you're either there for 5 years (I'm stubborn) or forever. Not a lot of in-between.
There's also a ton of attractions. San Fran is great to visit and tons to do. Sac has Old Town - a tourist thing, but still cool. Theater life in Sac is pretty good, and San Fran is even better. Monterrey Bay is nice - go for the aquarium rather than the shopping. There's all the national parks which are worth the trip. Muir Woods outside San Rafael is great. North up I-5 is the Avenue of the Giants. I didn't go south much, but Disney is down I-5, there's various amusement parks, Hollywood, LA, you get the idea.
Bottom line - I am never moving back to California. You may love it.