What's the verdict? Well, I think this trade was a win for the Islanders. After all, they're trying to compete now, and the 13th overall pick doesn't help with that (none of the players drafted outside the top 10 have played a single NHL game yet, except Owen Beck, who played one).
In exchange for a pick which might turn into a very good player, but not for another few years, the Islanders got a hard-hitting defensive defenseman. His stats outpace his advanced stats, which is something to keep an eye on. But when he's on the ice, the Islanders score more.
It's also important to remember that Romanov will be here for a while.
He's still only 23 years old, and has two more years on his contract (at a very reasonable $2.5 million AAV). When that contract expires, he'll be a restricted free agent and will sign back with the Islanders. Realistically, there's no scenario where Romanov isn't an Islander until at least 2027, unless the team decides to trade him. After all the turmoil of the Chara/Greene season, having stability on the blue line isn't something to take for granted.
Plus, he does things like this: