Well so seems i could have to say smth. too.
Ive been playing sc2 since beta, so here some things i noticed so far:
for the old starcraft players.. if u were good u can still be good in this game.. old strategies seems to be possible (for example dark templar rush etc.).
On the other hand the new "rush" nation seems to be the terrans with there jumping-over-walls units.
There r still some things that might be overpowered like a fast tech to air units or the protos "stalker"

For new players:
Like bonyv said it is okay if u like and know some strategic games like those mentioned.
there will be a hugh difference between campaign gameplay and "real gameplay" online in a skirmish match but anyway some pros:
- realy nice campaign that wants u to play it till the end (maybe a bit to much linear for my taste

)
- blizzard has a good reputation and make good games:
They r known to support their games online and always bring in new patches for everything (not like THQ <- they do nothing after selling their products).
If u like the "standard" u might get one of the best strategic games in the future... sc1 was good... sc2 seems to have a similar gameplay and is more "modern"
If u believe that u might loose your interest in the "standard games" to fast, to be worried. with warcraft III (as "newest product") we know that their r much fun games that r so much different from the basic game but can hold u for a long time. And for sure u will fine the "good old ones" and many new ideas their soon (anyway their r already fungames there

)
So like wc3, sc2 will be a game with a long potential for many players.