We saw the worship of Lord Shiva in Ayodhya, Mithila and in Lanka as shown in SKR. In Ayodhya, Sumitra did pooja to Shiva Linga, in Mithila, King Janak and all worshipped Lord Shiva in human meditating form and in Lanka, Ravan and his followers worshipped Nataraja. Why the same god shown as worshipped in different forms?
I read about Lord Shiva and his forms before commenting here. Yes, the hero of the story is the supreme and he/she is worshipped by all others. So I don't want to go into the story of Linga rupa from Maharishi Bhrigu or Brahma-Vishnu fight. Yes, for me brahma and Vishnu are not immatured to fight. Just let us leave aside and focus on the topic of concern.
I have few reasoning for such a difference in the portrayal of Lord Shiva.
Linga Rupa: Linga in Sanskrit means symbol or sign. In Shvetasvatara Upanishad, Lord Shiva was shown has no linga, symbol. Shiva linga image denoted the Union of shiva and shakthi which is the highest state of existence. Shivalinga represents the Ultimate reality, the Brahman, the Paramatman.
-> So Sumitra from Kasi, worshipped Lord Shiva in Linga rupa (while everyone worshipped Lord MahaVishnu) who got the divya dharshan of Vishnu in Ram.
Meditating Rupa: The ultimate supreme power is represented as none other than a normal human being in deep meditation. His trisul represents three gunas, Moon in his head indicates that he controlled the mind, flow of Ganga signifies the nectar of immortality, wearing the skin of elephant shows that he has controlled his pride, sitting on tiger's skin indicates that He has conquered lust, wearing of serpents denotes wisdom and eternity, third eye is the symbol of wisdom.
-> Rajarishi Janak worshipped Lord Shiva in human form with control over all itchas. One thing, they missed Goddess Shakthi (Sita asked for Gauri matha statue but they didn't show it yet). Yes, Janak lead a life of rishi who realized the truth of life and saw god in each and every human being.
Nataraj Rupa: Lord Shiva adopted the form of Sri Nataraja - the Lord of Dance and performed the cosmic dance of Tandava. He performed the dance to suppress the immortal demon Apasmara by crushing him with his right foot. Here Lord Shiva is shown with the power of destroyer. Though he involved in destruction of evil only, the symbol of nataraj is expressing the mighty power.
-> Ravan believed in his mighty power than his knowledge. Though he mentioned himself as a great Shiva bhakth, his bhakthi was proved by his mighty power. So he was shown as one who worshipped Lord Shiva in Nataraj rupa.
Note: This is just my POV. My understanding of Lord Shiva is very limited, so I am open to accept any different perspective for the same.