Instead of simply telling you what I'm excited about (everything, lore wise leveling wise and graphics wise, plus nostalgia), Why don't i simply tell you what i would do if i got in?
First, i would have to double check to make sure it was real. Look at the webpage, check my email, look at the specific Cataclysm account and make sure the key worked. Then, it's time to download and patch up.
As soon as that patch is done, it's game time.
First thing i would do is immediately create a Goblin. Let me tell you, i would create the CRAP out of that goblin. I'd go with all the weirdest combination of facial expression, hair, and skin color. Why? Because I'm in the beta. Anyone within earshot would no doubt attest my maniacal laughter as a sign as of my insanity as I swapped through the various skin colors of the Goblin, each one increasing my volume 2 fold until i managed to get the most out of whack one.
I would be unable to hold back the squeels of excitement as i pressed "Enter". Each little bit the bar progressed to the end would make me crazier and crazier. As soon as I'm in, ALT TAB.
Yeah, ALT TAB.
Quick as a whip, I pull up the Cataclysm account management page. There is no time to waste in my own little world at this point. I copy my Druid and premade a warlock and shadow priest ASAP and get the ETA asap, although i won't be touching them for a while. Then, ALT TAB. No time to waste!
As my squeels are coming out in quick succession, I would begin to do hardcore testing on the Goblin starting zone. Not a single foot of ground would go unwalked on by me as i feedbacked every single quest. Not one letter would go un spellchecked, not one mechanic unviolated by my insane scrutiny. I would zip through the zone as a rogue, and immediately head over to the Forsaken areas.
Low and behold as many loregasms would be had as I pretended my goblin had been recently revived by Sylvanus, and I was simply serving my Dark Lady. I would kill and crush as though i were crushing players on the other end, and i was /point and /laugh at any corpse I found.
Break time.
Breaking into a full sprint, I rush to get some water. I pull out a large sized cup, press the refrigerator to the water setting, and begin pouring. I would be hopping up and down, causing the water to spill out over the cup. No time to worry about it. I get 3-6 medium sized icecubes and sprint back to the computer, spilling half of the glass on the way up.
Oh well.
I would frantically regain my position and return to my squealing as i continued to quest like a maniac, rushing through 1-60 while being as thorough as possible on the Eastern Kingdoms, and then doing 60-80. Of course, I would be squashing bugs.
And how so.
I would have to be kicked out of the beta due to my rapid succession in finding bugs, the CMs and Devs no longer wanting to deal with my reports and feedback on the forums and ingame and wanting some new players to give feedback. The other players would hate me for squashing bugs before they could.
Nothing I can do, haters going to hate.
I would proceed to pimpwalk past all of them, and if I see any stopping to report a bug or feedback a quest, I would slide on up to them and whisper "I already beat you to it" and then gallop off into the sunset on my various mounts. This would continue until I was removed from the beta. Once i realize what they had done, I would sit in my room and begin plotting to regain access to the beta, knowing full well that once i returned the beta servers would face a testing the likes of which had never been seen before.
And then i would eat some oats.