I've never seen my med pop server dead. Never seen max level zones empty. Never been unable to get a group.
I don't pvp
Leveling doesn't take too long. 2.5-4 days for someone looking to get it done. Up to 7 days for someone looking to savor the experience. Numbers are with leveling tradeskills. They generally aren't hard to keep on pace with your level.
2 twenty man raids right now, we're about to get a 10 man raid opened up. Plus rift raids. They are somewhat similar. As was mentioned, the bar for endgame starts a little higher in Rift. endgame dungeons are harder than what WoW throws out. No hardmode raid fights though, so WoW probably has the most challenging fights of the two if you seek them out. One of the biggest differences will be group/raid makeup. You shift your specs, you can have 4 now and soon it'll be 5, according to the fight. You have support buffers, debuffers, bulk healers, precision healers, and you'll typically be switching out who tanks what depending on the mechanics.
Never had a problem with controls in DAoC/WAR. UI is extremely flexible in Rift.