As interesting as I find the current state of deep learning to be, there is something about random forests that I can't help but find much more cool. Probably the amazing out-of-box performance.
"Greedy function approximation: a gradient boosting machine" - JH Friedman
I also once started implementing a R package for "partial dependence plots" [1][2], which are popularly associated with Random Forests but aren't specific to them.
[0]: https://CRAN.R-project.org/package=forestFloor
[1]: http://scikit-learn.org/stable/auto_examples/ensemble/plot_p...
[2]: https://github.com/gwerbin/statsplots/blob/master/R/partialp...