If you like traveling without a guide in other countries and find this satisfying, the same will be true in Moscow and St. Petersburg. Of course it's not either/or - you can certainly take a guided walk or boat tour, for instance.
I cannot emphasize enough the importance of learning Cyrillic if you're going on your own. The book I used was Teach Yourself Beginner's Russian Script, which was great. It breaks down the alphabet into letters that are the same as English, letters that look the same but are pronounced differently, etc. It's out of print, but you can get used copies on Amazon: http://www.amazon.com/Teach-Yourself-Beginners-Russian-Script/dp/0071419861/ref=sr_1_2?ie=UTF8&qid=1459701143&sr=8-2&keywords=teach+yourself+russian+script
Russia is indeed a bit more "foreign" than say, Italy. However, in Moscow and St. Petersburg, I found enough English to be able to get by. Many restaurants had English menus and/or English speaking staff, for instance. This was most emphatically not true in Vladimir and Suzdal (two cities in the Golden Ring outside Moscow). I went with my sister, a Russian speaker, and if she hadn't been there, I would have been in big trouble. So, if you want to see places outside these two big cities, use a guided tour (even if just for that part). Also, Moscow and St. Petersburg are huge cities. Coming from New York, I wasn't intimidated, but those not used to a megacity may not be so cavalier (even I found them overwhelming at times, especially Moscow).
I found both Lonely Planet and Rough Guide to be helpful, and both to have various errors. Look at both, buy whichever one has a more recent edition, and then be prepared to have to discard some of the advice therein. Also, these places change more quickly than places in Western Europe. Be very careful of outdated advice. For instance, I was there in 2001 and 2010, so I won't give you any specifics on getting a visa - that changes constantly.
Just as a teaser, two things I saw and loved that I doubt would be included in any escorted tour are the Gorky House in Moscow (an Art Nouveau wonder) and the Sheremyetov Palace in St. Petersburg (it's now a museum of musical instruments, and the decor is amazing, particularly in the Etruscan Room).