See, I hate it when a company designs a game and when one part of it is good and another is ****, the game is still considered good. WarCraft3 multiplayer is amazing, yet single player sucks and the reviewers give it 9 out of 10. So why shoudnt I release a game with amazing graphics but have the gameplay suck and still receive great reviews because one part of the game is good.
Single and multiplayer are two facets of gameplay; you cannot directly compare having good graphics and bad gameplay to good gameplay and mediocre gameplay.
You have to remember, single player experience will be 0-20 hours for most players on warcraft 3 -- and, as i've said, most of my friends have not finished the single player but jumped right into battle.net competition. This will give them 200-1000 hours of playtime, at the least. Starcraft gave us even more.
Games generally don't get panned by reviewers if their graphics are anywhere near acceptable and thanks to the good artwork, WC3's graphics are generally above acceptable. Graphics aren't as important for immersiveness in an RTS game as they are in an FPS game.
To be honest, I thought WC3 was really shallow at first when i started playing the beta online. The beautiful thing about warcraft 3 turned out to be the dynamics between people online when competing: there are just so many things you can do with a hero.
Granted, the general units are much more limited than they were in SC, but the gameplay focuses around micro-managing your hero. I like it far better than I did when i only had a few hours of experience online with it.