Probably the most notable to the western ear and tounge are the 'r', 't' and 'd' sounds. There are three different sounds that sound like 'r', four 't's and four 'd's. At first all sound much too similar. With practice they can be differentiated and mastered. Once the alphabet has been learned, one can fairly quickly and accurately read and pronounce Hindi.
Hindi grammar is another story.
It might be best described by an American as inside-out from English. This isn't too difficult in itself, but when you begin creating longer sentances it gets a bit more difficult to translate. Any verb might be presented in dozens of different forms. Working with a good language school or tutor, the average person can handle rudimentary Hindi in a few short months. To speak fluently is a matter of years.