In terms of PvP area, Daoc was still considerably larger, however ESO is definitely larger than most other MMOs PvP areas. Also, it should be mentioned that the ESO pvp area is very detailed with all manner of interesting areas and terrain besides just the keeps and castles. Its also great to see Daoc style milegates back again.
Latex is quite right about the lag, I was involved this weekend in many large fights, often with a couple hundred people fighting each other and it all ran lovely and smooth, even with all my settings on max.
One thing I should mention is that I hope that the player base gets out of its modern MMO mentality and gets more into a Daoc PvP mentality. The milegates in ESO are very similar to the milegates in Daoc, and people need to start using the terrain and strategies that were used in Daoc, rather than just running about in a zerg like more recent MMOs have done. Sadly in the beta people did tend to get sucked into the modern MMO zerg and run from castle to castle, hopefully once release is here we'll get some Daoc style stay and defend/garrisoning chokepoints going on too , to supplement the main force.