Despite his showing against Calgary over the weekend, Nurse is a legitimate #1 defenseman and has been quite good this year. That contract is horrendous in that it will likely age terribly, but it's not really that insane for this year.
OEL is a #4-5 guy who as Jannik Hansen said on Vancouver radio, wouldn't be that bad if you didn't know about his contract or his previous play. However, those things are reality, and he's a shell of his former self, and on one of the very worst contracts in the NHL.
However, this trade makes absolutely no sense for either team directionally. Vancouver would maybe do this because they'd have to pay a 1st (and likely more) just to get rid of OEL's contract. To get Nurse at a market value contract is a great return. But it doesn't push the needle enough for the current team, which is mediocre, and might just be better off keeping the 1st.
Edmonton is getting smoked. They have absolutely no reason to trade their best defenseman for a mid 1st round pick and to take on one of the worst contracts in the league while they have two of the best players in the world.