The Chosen have too many Meltaguns and too many guys in the squad - five dudes with three meltaguns will still kill pretty much any tank you care to mention, so save the points. Lose Lash and Mark of Slaanesh on the Prince and give him Mark of Nurgle - you want the Prince in combat, and Lash is a shooting attack, so you're wasting Lash if he's in combat but you're wasting his raw stats if you're out of it.
If you drop some of the havoc launchers and the greater daemon you could take a defiler, which I'd prefer to go for.
He has blast weapons in the Havoc Launchers, and the Greater Daemon is a more credible threat in close combat than a Defiler due to the all-important Initiative stat.
Also I disagree about death guard in close combat... They're overpriced because its an old codex but they all have two attacks get wounded on 5's for most things, 6's for things like dark eldar and guard (and anybody who thinks guard are bad in CC should try charging a 30 man squad and a commissar with a carnifex... ), then you have essentially a 2+ save from FNP. The only big downfall is a slightly lower initiative, but imo that just makes the power fist all the more sensible for them.
Being tough and having more than one attack doesn't make you into a good combat unit. Berzerkers are 'good', with four Strength 5 Initiative 5 attacks at WS5. Plague Marines, which strike at I3 with low numbers of attacks that allow saves (despite having 2 attacks each, at 23pts a pop you aren't getting many dudes). Plagues can tarpit units until the Daemon Prince, Greater Daemon or Terminators arrive to help them out, but they won't win combat alone.
I mean sure, they're not designed to be a CC unit, but they're a damned sight better at it than most marines.
Except they're not really. They have a low model count, and have an extra attack at the cost of one initiative. They aren't good in close combat - they're good at sitting there and absorbing hits, doing minimal damage of their own, until someone turns up to rescue them. Paying 40pts for 2 swings with a Power Fist doesn't make them any better - REAL assault units will beat you up, Fist or no.
Let me put it this way - how scared are you of vanilla Assault Marines? That's slightly more threatening than Plague Marines in close combat. Initiative is a vitally important stat that should never be overlooked.