Vileplume, along with Magnezone, is one of the few Stage 2 Pokemon left that sees serious play in metagame decks. Like Magnezone, one of the reasons for its play comes in a powerful special ability, the Poke-Body Allergy Flower, which shuts down all trainers on both sides, regardless of whether Vileplume is active or benched. This makes Vileplume's trainer lock extremely difficult to remove, as the only ways to drag out Vileplume lie in drag based attacks like Bellsprout or Muk. Weakness isn't a huge deal since Vileplume is rarely dragged out, though it means that Mewbox can carve through it if Vileplume can't retreat after being dragged into the active spot. Its HP is alright, but within the magic number if it ever finds itself in the active spot. Dazzling Pollen is pretty terrible and I doubt it's ever been used barring the most desperate of circumstances.
Vileplume's biggest and best partner is Reuniclus. As anyone at Worlds 2011 might tell you, the lock with Vileplime/Reuniclus can be game changing, making it nearly impossible to take KOs. This changed to a degree with the release of NV making Lost Burn more abusable, but unlike Gothetelle, Vileplume's lock is rarely at risk due to being on the bench, meaning it can rely on other attackers to accommodate. When ND comes out, Vileplume might be able to survive the power creep by using Regigigas EX, which is basically a heavier outrage sponge that could OHKO other EX pokemon. One thing that's risky with this however is losing two prizes in a deck that already sacrifices prizes early. It's viable, but has its drawbacks. All that aside, trainer lock is pretty crippling on its own, especially for evolution based decks. Shutting off Rare Candy and Pokemon Catcher is a really powerful tool and that can't be stated enough. Vileplume can make some mediocre decks very dangerous, one such being Chandelure.
Right now, Vileplume is definitely 9/10 territory. Not everything can use it, but enough decks can harness Allergy Flower and put a real kink into everyone's game. It may yet survive ND despite my earlier predictions, though I think its best days are behind it (its really hard to beat two borderline autowins against two big decks at the time). Vileplume has few bad matchups and has a chance against any deck, all by simply locking trainers, which can show just how dependent on them we've become.