I put off watching this because I've all-too-often found fan-made parodies to be just plain terrible. This blew my mind, in the best possible way. However, it's not without it's downsides- the worst in my opinion being that version on youtube has rather bad sound quality, meaning it's hard to hear the characters speaking (though songs are usually better). The others are very
minor, and also very
unavoidable (mostly consisting of legal issues and practical issues), so I won't list them.
In my opinion, the sequel is much funnier than the original, though it's very important to watch Musical before Sequel, otherwise there's so many in-jokes you simply will not get. Like Draco's monologues. Oh God those monologues.
All in all, this is a brilliant series, mostly due to the insane characterisation of... erm, everybody. Lupin, Draco, Umbridge and Lucius are the most interesting
reinventions. Most characters have their traits in canon upped to eleven, for example, Snape is actually more hammy than in canon, Dumbledore makes a pride parade look closeted, while Ron and Harry are all but twins (in terms of personality and bromance, not looks).
All in all, I'd recommend for everybody to at least take a look. I just wish I'd discovered it sooner.