I think Paras and Parasect are very underrated. They both lost some of their uniqueness when Spore, their signature move, was made more accessible. Shroomish is generally really liked and Foongus and its evolution are quite good during battles as well.
The Paras line, however, still suffers from its Bug/Grass typing. They got some good moves like X-Scissor, but that's nothing new, really.
It's a shame because those two have some really nice concept behind them resulting in some very dark lore bits for the Pokemon world.