I started in the beta, but stopped playing sometime around 2010 maybe? After CoV, after AE, before 2012. My first kid was born in 2008 so everything's a blur after that. Two things that stick in my mind:
Everything was slower in those first years. Literally, because you couldn't get your travel power as early, and also progress-wise. I don't think Patrol XP existed even, so getting a character up to 20 and beyond was truly work. This is pretty normal in my experience with MMOs, before they get tuned appropriately, but it means that the MAJORITY of my memories from that time are lower level content.
The second was brought up already, but it's HERDING, before the max aggro limit. I remember our team of 8 Rad/Rad defenders herding up whole maps with Enervating Field and Radiation Infection, stacking all those debuffs on hundreds of mobs before wiping them out (much like Vortex + Archons for any Starcraft players out there). It was just really satisfying.