I'm not saying it's not still good. It just isn't as omgwtfbbq as at level 1. Do note that Freedom of Movement has been available for some time at level 16, though.
True, but that's why I was saying it depends on the encounter. If it's a caster whipping out Freedom of Movement, I'd be more worried about them tossing Dissintegrate or some Save or Die spell at me. I'd lump them in with the ranged attackers I warned about.
I'm thinking more along the lines of Big Dumb Fighter -types. They are just as crippled at 20th level as they are at 1st. If the NPC standard treasure affords them a Ring of Freedom, then all I can say is.... LOOT! If a DM uses advanced HD animals, or other not-so-intelligent combatants, then I'd constantly keep entangling in place whenever possible.
I also like the thought of using entangling as the poor-man's Fairy Fire. Act as a spotter and coat the hidden or invisible bad guy in fiery entangling goodness.