one think i like the most about rift is the non instanced event. and invasions.... now thats what i call massive... still buggy tho, last night i joined invasion group against huge war golems... killed 1 and the next one we got it to 1/2 hp then it suddenly disappears and respawned in full hp... decided to logout right after.
and you can get overwhelmed lots of times in this game... mobs can spawn on top of you endlessly.... which i don't really like. engaged 1 mob another 2 aggroed, killed 2 of em and another 2 spawned and instant aggro.... you know what happened next....
also the one scott hartsman mentioned regarding smart engine that can detect number of players in certain areas... well i got a bitter taste part of it... i was alone in an area with just 2 or 3 mobs around.... decided to engage 1 of em, then a group of players came... suddenly the whole room was packed with newly spawned and aggressive mobs... again you know what happened next.