A great addition to an already awesome game, just too short. The greatly improved multiplayer really makes it a blast.
The single player component is a little bit on the weak side primarily due to this issue of length/variety, but where this game shines is the multiplayer aspect (which was great in the original as well), as the new missions are extremely conducive for great matches, particularly the bridge defense/destroy map, which felt perfectly balanced for both sides (granted if both teams were good enough) making it a fun and dynamic map allowing for a large variety of play styles. More or less, it could be said that it played a lot like a larger 2Fort map, but with far more cover.
However, because it is H&D2, good luck getting it to work on your computer (won't start in Vista), and even then the likelihood of there being anyone or any servers is extremely unlikely.