Dreamcast: loads of good games, online play, lots of AAA titles anounced (including Max Payne, half-life, Black and white, Halo DC etc). Also good developer support (such as Valve, Bizarre games, Team ninja). Good graphics as well.
Ps2: Expensive, pretty crappy starting line,up, typical sony hype (emotion engine!!, ps2 will replace your PC!, look at our stupid renders!!), basic graphics (1st gen games), low availability.
The reason why the PS2 launch was so succesful was because of hype. The proof that it worked is the fact that most people now think the DC is crap without valid reason. Granted there were bad things with the DC but lining up the facts, it was clear which console was superior at the time and which "should" have sold more. The same is going to happen this year with the PS3 no doubt, except this time M$ has money, which Sega didn't after the crappy sega saturn. Sony is not stupid, we might think that the PS3 is all hype but the average consumer will believe it.