Not only is Foursquare's recommendation engine great; the lists are awesome. It's actually been sad to see them gradually make lists less visible. At least, they still have the TODO list which gives me an easy way to find a place I have been meaning to go. On the venue profile, they used to feature the lists that users made containing that venue. So what I would do is find a place I like and then I could easily find other places based on the list's it was a member of. It makes traveling so much more fun.
The whole social thing about Foursquare is it's weakest point. I don't know why they are emphasizing it so much. Firstly, only an extremely small subset of my friends are on Foursquare and secondly I have enough social networks.
Yes, because of Foursquare I ran into some friends in my neighborhood that I would not have otherwise. But really that's not nearly as cool as the random hotel costume party I found that was trending one night. Or the countless coffee shops, bars and restaurants I discovered while traveling.
So to me the strengths of Foursquare are: * Recommendation engine. * Lists ( TODO and Public Lists ) * International usage. * chance social encounters with friends.