Well, the overall concept is fairly simple to understand, and beginners have a set of recommended items, to understand the idea of an inventory build at least at a basic level. Then there's the tutorial that will further explain the gameplay mechanics, which you can go through entirely or selectively, depending on how much you already know about the game.
The only real compelling argument for getting into the game now comes from that group of friends who spend hours a day playing, telling you how great it is until you finally give in and join the madness with them.
Heroes of Newerth is a multiplayer RTS based on the classic DotA scenario for Warcraft 3, so it comes with a classic gameplay, a great number of characters and hundreds of items that you have to know and try in order to win a match. It can be a very though experience for all newcomers, as they need to play several matches only to know how to use some heroes.