Pros
The coordinator, Laura, is a great boss to work for. She's reasonable, hard-working and fair. A lot of the home-stays are located near the school, so you can get a nice, neighborhood feel about life. I recommend Jenny's place. The students are also great. The Costa Ricans are warm people with great personalities.
Cons
Depending on your schedule, sometimes the work-load can feel heavy. It's important to share your expectations (and work hard to prove your deserving of them). I worked everything I was given the first few months, and never took off a day, so that as I built seniority and reputation, I could use that toward working with management to get a better schedule that suited my lifestyle better. However, if you come into the job with an idea that you'll get weekends off, and all vacation days, you are wrong. Just like any professional setting, these people need reliable workers who aren't trying to take vacation every other week. It's hard, as you're in Costa Rica and San Jose doesn't do that country justice for what it can offer, but they're running a business and they need professionals.
There is a lot of turnover and a lot of first-time teachers. This takes its toll on administration and students alike, but if you're committed to the job and your contract (I stayed 1 year) you can build a really great relationship with the school and the students. Keep in mind, this is a professional job, and if you treat it as such, you will maintain the standing you need necessary with administration to be able to use your schedule and time-off in beneficial ways