The Frozen Throne has a great campaign storyline, full of twists and thrills. Be sure to finish all of them.
All four races, after patch 1.26, are (nearly) perfectly balanced, take your time using casual account to discover which fits you the best. Try 2v2 games, both micro and macro are essential in the scale of match, making WC3:TFT melee the most enjoyable games ever.
Also, you might wanna check out the following website for AMAI----Advanced Melee A.I., these enhanced bots created by devoted fans can simulate real person strategies, have fun practicing with them.