You really have to do your homework with rentals. Know the laws, know how to crunch the numbers, know the most common headaches and reduce the chances of seeing them. Join a forum like biggerpockets, read their daily blogs, and listen to their podcasts.
Bought my 4th multi-family in/around Boston in October. I'm a school teacher by day and real estate has been my path toward financial freedom. It's hard work, but definitely pays off (for me personally at least) and can create real generational wealth.