Impossible to pick one, but if I had to put together a list it would probably start with GW2 or WAR. DAOC is all time favorite MMO, and the fact that nobody has managed to put together a worthwhile game based on that design since really bums me out. GW2 especially looked great at first, but everything about it was just a bit off - the combat felt weird and clunky, the WvW was terribly designed, the map design sucked, there was no real progression, etc etc.
Second up is Diablo 3. They've managed to make it at least playable now, but it will never be a worthwhile followup to the first 2, which were both such a huge part of my early gaming years.
DA2 definitely needs to be in there too - I wasn't as in love with DA as I was with the Baldurs Gate games, but it was still an excellent RPG that I had a blast playing, but they absolutely obliterated any potential the series had with that godawful sequel. That was just straight up terrible game design and anybody who worked on or signed off on that project should be blacklisted from the industry.