But the old StarCraft isn't perfect!
Pathfinding is useless, you can't set flags from buildings so workers automatically start collecting when they're built, you can only select 12 units at a time,... And that's just ingame stuff. Not to mention things like matchmaking, which makes sense in a game as popular as StarCraft with the skill-gaps so wide as in StarCraft.
StarCraft 2 didn't just modernize the graphics, it modernized StarCraft.
Is it something entirely new? No, but if you liked Starcraft you'll probably like Starcraft 2 too once you're over the "this is different, I don't like it - this is the same, I could just play the old one" phase.
It's a bit like Windows 98 vs. Windows XP/Vista/whatever-new-OS-you're-using.
I'm not too big on rts games in general so I'll wait for the campaigns to come out in one affordable pack before I get into this game. Lack of Lan play sounds pretty horrible too.