I re-bought this game after playing it as a kid. It's often dismissed as a Warcraft clone but it actually has a lot to offer. 3 campaigns, 3 races, a map editor and a whole bunch of single maps to play on, plus multiplayer support. The game itself is good fun and includes RPG elements such as levelling troops, which you can "save" between levels and "hire" later on. Love the music and graphics. For me, it's a classic, but that may be due to a significant nostalgia factor.
Downsides are that the game is very old now, and as such the multiplayer support is poor (difficult to set up, sometimes crashes), there's no support for resolutions higher than 1024x768, and incompatibility issues with Windows 7 sometimes manifest in strange ways, like your troops becoming very slow (or sometimes completely unable) to heal over time.
I've been searching around for the source code for this game in order to try and rectify some of these issues, but to no avail.