I don't remember the upgradse. It sounded like many of the things that were patched or added in the expansions for two made it to 3.
However, there is a wikipedia page dedicated to Sims 3. It should have all of the information you want. That can be found here:
http://en.wikipedia.org/wiki/The_Sims_3
Gamefaqs has it rated at an 8.9 right now if that means anything to you.
This link will take you to the gamefaq forums for sims 3. You may be able to find a better answer there than here.
http://www.gamefaqs.com/boards/gentopic.php?board=936498
On digital downloads: MOST places will give you a warranty on the product you download. For example, so long as Steam/Valve are in place, you can redownload any game you have purchased, ever, forever.
I HAVE NOT CHECKED THAT THIS APPLIES TO EA BUT, I know they have a program for digital downloads, as well as a website that you may be able to purchase from, and the last game I purchased from them had a two year redownload warranty. So I could redownload it as much as I wanted over the course of two years, but after that I no longer had the right to download the game. Whatever website you use should have their policy somewhere, and if they don't have one I wouldn't download from them. I also felt short changed by EA (they're the same people that make sims btw), but was too lazy to get up and go to a store for the game I bought. So yeah.
But to answer the original, actual question, I haven't tried Sims 3 yet, so other than the info I provided, I can't help you out.
Etc. - Oh, I'm a gamer, btw. If you need info on games, let me know.