I first started playing warcraft 3 years ago when I used to still LAN at my local center. The game itself didn't really grab my attention - but the custom hero games and tower defense games did.
The beauty of custom games are they are constantly evolving - by the time you get bored of the latest custom game - the new thing is already in the pipe works and ready to be launched. The rate of release of custom games has diminished over time with map makers spending time on other things and the over all play of Warcraft 3 dropping off with WoW but you still see gems being made on a consistent basis.
After saying that - the game itself is great. It's probably one of the best strategy games out there - with heroes bringing a distinctive flare to the table. The missions are tedious at times - but I beleive they are there to teach the basics/intermediate skills rather than provide a true story line (the same is not the case with the expansion pack - the frozen throne).
Now is a great time to pick up warcraft 3. You can familiarize yourself with blizzards make maper before the new star craft comes out and at only $19.95 it's a great stock filler/present for your child to give to one of his mates.