I don't think it's a language in its own right. In Belgium and the Netherlands it's considered a dialect (though I'm aware of the fact the distinction is quite arbitrary). People speaking Dutch are perfectly able to understand Limburgs (apart from some words that are specific for the region, like Sjoatelsplak for vaatdoek, dish-cloth. But this is a common characteristic of about every (Dutch) dialect I guess), though pronouncing it might pose some difficulties to most. The use of /ʁ/ instead of /r/ and the singing are the easier aspects.
Since Limburgers tend to speak more slowly and singingly it's a common joke among Dutch speaking people to consider them slow-witted. But then again, every dialect has its stereotypes (at least in Flanders). Mine makes me a peasant, for instance. Fun galore when talking with people from all over Flanders!
Fluent: English, French
Learning: Swedish (when I have the time and the energy)