I don't know why I got a beta invite, nor do I care. I registered at http://www.charlieoscardelta.com a month or two ago, but never did anything with it. I'm going to assume that I'm being rewarded for all of my strength of character and good works.
Onwards to the beta impressions:
I like it. The perks add a nice dimension to the gameplay without providing "power weapon"-style advantages. The gameplay retains the feel that I loved in CoD2, and is miles away from the dribble that was CoD3. On a completely unrelated note, I have a copy of CoD3 available on the cheap. The move to the modern era works very well, and I find the increased weapon selection to be a welcome change. The melee kill is one of the most satisfying multiplayer moments that I have come across. No longer shall be satisfied simply bashing an opponent. I need knifeage from here on out.
The challenges have been my favorite addition so far. For example, if you get 25 kills with a specific weapon, you get a red laser sight that you can attach to the weapon. This made it much easier for me to find my target, but doesn't provide a tremendous advantage over a player who doesn't have one. Other challenges produce similar upgrades or extra camo skins for your weapons. One cool feature is that if I kill someone and pick up their weapon, it retains all of their modifications and camo. It gave me a chance early on into the beta to see how the upgrades worked, and that made me want them lots and lots.
Ranks are gained through hitting traditional experience point milestones. You get exp. by killing folks, completing challenges, and completing matches. Additional perks, weapons, and game features open up as your rank increases. Ranks are (as of the time of this posting) capped at 11, but there were some rumblings that this will be increased throughout the beta.
The other cool feature (unlocked at a rank of 3 or 4) is the custom class. You pick your primary and secondary weapons (including any modifications), and three perks of your choosing. Once I got to choose my perks to fit my play style (I suck, so I need extra health plus deep impact to shoot through walls), I found myself enjoying an engrossing play experience even more.
Prior to playing the beta, I had relegated CoD4 to "bargain bin purchase only" status. CoD3 had left a bad taste in my mouth (I know it was another developer, but it still had the CoD name on it), and I thought the genre was stale. I was wrong. I am enjoying the hell out of this game and have moved it to "already pre-ordered" status. Good luck to everyone on gettin them beta tokens.