Hello,
I have been playing the beta for like two months or so and Starcraft 2 has turned out to be "the new RTS" for me after many many years of EE and when the game hits retail I hope to see some old EE faces there too
The gameplay has improved a lot from SC1 so if you haven't played old Starcraft before at high levels, you won't be that much behind if you swap from EE to SC2. Many things like CTRL-move and grouping units and buildings are similar in EE. Almost all of the common EE hotkeys are different in SC2 but it doesn't take that long to learn them. Game still relies heavily on micro/macro game, economy control, unit producing and army control like EE. There are also some "cheesy" strategies like floating your barracks into opponents base and making marines there as terran, something similar to EE's forward rax rush, or as protoss making photon cannons in enemy's base to block mineral gain, similar to tower rush in EE. Many different ways to win a game, EE micro skills will definately help you in SC2 too.
There will also be a ranking system for 1v1/2v2/3v3/4v4 with 5 different leagues (Copper/bronze/silver/gold/platinum) that will be divided into divisions with 100 players each. You will be put into league after you have played 5 or 10 placement matches, after that you can go down/up depending how you play. You will get a notice that says: "You have been moved from X league to X league" after a game. Top-8 players of each league will be in end-tournament in the end of each season, and maybe receive some award to their profile. Not sure about that since there haven't been any end-tournaments yet.
Some of you might thing what are the computer specs you need to run SC2? For ultra high graphics you are going to need a new a brand computer to run it smoothly but to run it on low-medium graphics (still pretty good looking) you won't need that new comp. I personally have computer from 2006, bought for 400€, with Intel Core Duo 6750, Geforce 7600 GT and 2 GB of memory and I can run the game well on medium settings without any FPS drops even with mass units. But if you are having problems running EE then you should think of upgrading or buying a brand new comp, it is absolutely worth it.
PS. If any of you got beta (EU), you can add me for some games

Name and idenfier (BoomeR.boomer)
inb4 wall of text crits you over 9000>_>