These games weren't designed to be played hours on end but some of them I got about an hour before I ran out of energy or whatever the game required. I find these games to be nice when I either don't have the time or I just simply don't want to get too involved in a game. Play a little and then come back and play some more. On face book I did have a few running at one time. As I said play a little come back and play some more.
My favorite is Farmville 2 on face book. I've been playing this since December I believe as I signed up for face book November of last year. I haven't spent ANY money on this game and I'm at level 52 now. I think it's kinda neat to have friends/family help you along. I did miss some of the goals but you can still go forward in the game.
The only one I ever spent money on was Farm Up at Big Fish. I bought some gold. I only spent the amount of a CE. No more than that and not because I felt I HAD to but I wanted to support the developer.
Do they want people to spend money on these games? Absolutely. Of course! I won't deny that.
I'm definitely NOT trying to change anyone's mind but this is just my opinion on the F2P games. Oh and yes I've come across some I didn't care for.