Well that explains the lag, you bought a plasma TV.
There are no real benefits to choosing plasma over LCD that are a good choice. Plasma TVs use more electricity, they don't last as long as LCD and they're more dangerous than LCD, not to mention far heavier.
You trade that in exchange for a few microscopial black levels of contrast that your eye probably can't even detect anyway.
As an example, my first LCD TV was a Samsung series 5, 32". It was not LED, it had 100,000:1 contrast ratio.
My second LCD TV was LEDLCD, it was 46" @ 50,000:1 contrast. This was noticibly grey, but still quite good on every other color. The TV was cheap, meh.
My latest purchase, which I am waiting on stock fulfilment, is a 55" LEDLCD with 300,000:1 contrast. It was $799AUD
By comparison, a similar quality Plasma TV costs around $2500