It’s still very much an emerging market, but it has developed a great deal in the past couple of years. I worked on launching an established brand in Argentina in 2007. It failed miserably because the only way players could deposit was in cash, at one particular branch of one particular bank in Buenos Aires.
You want to focus on Brazil at this stage. For whatever reason, the comfort levels of depositing via credit/debit card touch European levels there. This is not the case in the Spanish speaking markets in LATAM. Could well be a cultural thing, but this will change in time. My advice would be to build a Spanish site, add content where you can, but focus very much on a Portuguese/Brazilian portal, and on poker and bingo in particular.
One to watch in the next few years is Peru – they love a sports bet there.
BTW – I represent a LATAM facing brand. Drop me a PM if you’d like to know more 