I'm really enjoying the Beta. Best multiplayer experience of any Halo game so far. I'm one of those guys that complained about how much Halo 3 online sucked compared to Halo 2 (played it online since launch), but this blew me away.
The balance is really what comes down to making it awesome. I was afraid they were gonna overpower the magnum like it was in Halo (also feared Jet Pack would be OP), but they really hit the spot.
Invasion Slayer is very unbalanced in the Elites' favor, and I think Round 3 in Invasion could be easier for the elites (for example, by giving them more time if they won Round 1 & 2 faster). Other than that, I have no complaints - only praise.
I'll definitely be buying it on the release day, gonna go through the campaign on Heroic with my brother - and then go whack some on Xbox Live! 😀
My gamertag is Sandoar (if I have a negative KD spread in a game - it was my brother 😛)