I got my 20 tracks two days ago and I love the song, it is pretty tricky on drums when in easy mode.
A majority of the music is either mellow slower music (80's), old-school rock, a little bit of indie, cooler 90's stuff (more rockin'), and some nice 70's folk. About a third of the songs has to deal with love, other ones are about rocking out and having a good time. Out of the 30 (+ 20 DLC) or songs we unlocked, we don't like about 4 of them.
One is Alice In Chain's Man in the Box. It uses the name of Jesus Christ (screaming it) and backup vocals say "deny your maker", and some others have mild words in it (*ss, d*mn, h*ll, references to drinking and smoking. But only a small few.) But there are some more friendlier/clean songs, like Spirit in the Sky, talks about having a friend in Jesus. All the heavier songs have had their lyrics edited so you will get stuff hear on TV. As a fellow Christian, I like a lot of their song choices, but their are a few rotten apples here and there. But the whole Rock Band 2 kit (guitar/mic/drums/game) is going to set you back about $190 or so.
I suggest looking up both song lists and hearing the music for yourself to see what you do like.