After 5 hours of playing I have to say that I love this game.
First I have mention that no other rts that I've played (and there is good bunch of them) has ever felt this good. You go to explore the environment with scout unit, no enemies in sight... When the back up units are sent you can see first hostiles coming from the fog, shouting and soon screaming when your units pick them out one by one. Then other hostiles arrive, from left and right and you cover becomes death trap, preventing your units to form up to fight back. Will you take the risk to fight back, or will you send your units to fall back, which most likely will save them.
And thats just one fight, and might look like something that doesn't happen much likely, but it does. If the enemy wants to win, he either finds a way to destroy your defence or he tries to lure your units away. This gives truly the warhammer 40k feeling in the game, and when you game it just keeps getting better. Soon the walls that gave you so good cover are literally over run by tanks and walkers, making you run and hoping that you can soon pay them back.
I was waiting this game with thumps up so I might be bit too optimistic, so I'll try to gather here downsides too. First of all, I hated the current interface, not enough information or I didn't see it in front of my eyes. And minimap was just useless, half the time I was looking for units from there, until I gave up and completely ignored it, luckily they can still change that. There wasn't huge imbalance in the game, but I felt that all melee units were over powered. All they need to do is get into combat and your ranged unit is completely useless, when you reach higher tech levels it is really annoying to see your warp spiders fall when fighting cheapest possible tyranid units. Besides sometimes your units reacted very slowly to the combat, and even as it gives you change to surprise strikes, it is frustrating to see that some units don't react in far away fire.
About the preformance; I found it so good, that I was sure my fps calculator was lying half of the time. I used highest possible graphics, game runned perfectly with 50+fps and no matter what happened on screen, it was always higher than 20. There was rumour that vsync setting in game causes disables some smoothness, I tried without it and when I compared it to my earlier video material, didn't notice any huge diffrences. But as a note: I'm running with 8800GT and I have intel quad q6600 (which the game, thank god, is optimized) so its ment for gaming.
Units look great from the far, and only when you zoom to ''touch distance'' you can see some bad elements, but which makes the game again run better (when all the elements you are going to see look awesome).
Here is video about the preformance when full army of sluggas, the basic ork unit, fight full army of tyranid basic units (forgot the name

)
http://files.filefront.com/DOW2+2009.../fileinfo.html
AI was disappointment, don't know if it was on purpose for beta but it is done with purpose to beta, but it was horrible. Gameplay needs teamwork and AI was so lost with it, you can't tell it where you need those units and why, so mainly it was fighting lonewolf style, which doesn't work, at all.
There ain't going to be those huge scale battles that are in other rts, even though dow2 works very much like traditional rts game. Units cost just horrible amounts of resources, cheapest are around 300, while most expensive are about 1000 requsition. On top of that is the energy, so there ain't many times when you get to fight with more than 5 units.
About the races:
Eldar became my favorite thanks to their micro (building webway gates etc.) and their cool abilities (including warp spider no-gravity bomb

). Their weight was on end game. While their basic units are the worst in combat, and even their 2nd tech is average at best, you really need to get at the top of their tech tree. Thay are only ones in game that have ''epic unit'' in game, Avatar. It is pure ownage with 6000 health and damage that you rarely see. It is truly devastating sight in the battlefield.
Space Marines are the rambo style working super humans. Their basic unit is most expensive out of all, and only has 3 men without sergeant. I felt that they have too few units as a whole, because capping and defending was pretty hard when you didn't afford more than one unit in about 2minutes. They are simple to use, and their fights are always cool, I remember coming in with marine devastator plasma squad, and blowing my enemy's cover away.
Tyranids, simply what they are is one big horde of aliens. They trust in numbers most of all, but gain some really hard hitting special units too. I think that they are in beta, most over powered race, and pretty popular for that reason too. I didn't like them that much, but they've been waited to come into this game for so long that they are made just like they are supposed to. They feel like they are in tabletop game too, and hive mind voice was nice move from game makers.
Finally one more race from the orginal dow, orks. They also trust in mass and are the most ''fun'' to play out of all races. All that they have either looks or sounds funny, so most of the players don't think it is race for serious players, but that is where they are wrong. Orks can be devastating when using tiny or big army. They have (in my opinion) the best commander, commando. He gets straight away abilty to stun emeny squads for while, and that hurts in low tier.
Like I said earlier this is kinda optimistic look of the game, but next week beta will be open for everyone, and I really suggest to test it. This game needs teamwork, tactics and good spirit. Me like!