Hello everybody, nice to meet you!
My first impressions, hmm... well, I came from ArmA2 and enjoyed playing co-op, so naturally, that's where I put my focus on when I started testing ArmA3.
The first thing I noticed, though, is the technical aspect. The graphics look great and it runs quite good on my PC. I'm all for gameplay over graphics, but in this case, the graphics really add to the immersion. The animations, the shadows, the lighting... it all looks great. It has been a while since I sat in front of my screen, hands sweating and scanning for enemies, jumping a few times when my mates made a sound. And speaking of the sound, it feels like ArmA has grown up in that department. The gun sounds are great, movement sounds realistic as well.
I don't really know what to say about the gameplay. I know this seems disappointing, but... it's ArmA. One does not simply describe ArmA-gameplay in one post and do it justice. It's Bohemia milsim at its finest. The weapon attachment system made me squeal excitedly, the vehicle physics and ragdoll as well. Of course some things are lacking, like cookin grenades and all that, but I've read that this grenade system is just something thrown in for early testing, nothing wrong with that. You sometimes get stuck in the terrain (especially on the coastline), but that's stuff for the bugtracker. If you run into that problem, the vault-thingy (you know, pressing "v" in the standard control scheme) will get you out nicely.
But I have one major complaint: The compass. The size of that thing is a joke. Look at ACE for ArmA2, that's a usable compass. I can easily go "Infantry contact on 345." with that thing and my mates can turn around and find the enemy just fine. With this one, I have problems (that vary with daytime) seeing the numbers. If there's an option to scale the compass then I haven't found it. It may seem like I'm nitpicking, but I need that thing in co-op and so do many other groups. The compass is not only there for orientation, you need it for spotting!
Anyway, that's about it. Really great work on the Alpha, it works like a charm over here and we have good fun playing it. Thanks for reading my post, if you did.