A superficial examination shows nothing surprising or spectacular.The ragas used are generally rakti ragas like Kalyani, Shankarabharanam,Anandhabhairavi,Khambhoji,Shahana,Bhairavi etc.There should be some underlying reason for the musical genius of Muttuswami Dikshitar.
Dikshitar implicitly followed the Venkatamakhin sampradaya.Hence to evaluate his choice we have to adopt norms adotped by this tradition only.

In the Venkatamakhin tradition Bhairavi and AnandhaBhairavi were treated as upanga ragas.It is only later that they were treated as bhashanga ragas, necessitated by the usages of chatushruti dhaivata.For the purpose of our analysis we will treat them as upanga ragas.

The dhyana kriti is in Todi, a melakrata.Kharaharapriya was not included in the venkatamakhin scheme.There is no known composition of Dikshitar in Kharaharapriya.The twenty-second melakarta was shriraga in which the mangal kriti was composed.The dhyana kriti and the mangala kriti were in melakarta ragas.As the eptome of shrividya it was quite apt that the mangalakriti was set to shriraga.Of the nine navavarana kritis the under mentoned important aspects emerge from research :

a.The choice of ragas were thus :
1.Two melakarta ragas ( Kalyani shankarabharnam )
2.Three upanga ragas ( Shahana,Bhairavi,Aandhabhairavi)
3.Four bhashanga ragas ( khambhoji, punagavarali , ghanta and ahiri)

b.The swarastructure sequential change of ragas had quite some significance.

1.From Anandhabhairavi to Kalyani meant a change of Gandhara.
2.From Kalyani to Shankarabharanam meant a only a changeof madhyama.
3.From Shankarabharanam to Khamboji meant an addition of a nishada.
4.From khamboji to Bhairavi meant removal of the additional nishada, addition of a dhaivata and change of gandhara.
5.From Bhairavi to Punnagavarali meant removal of the additional dhavata and introduction of a rishabha.
6.The next song shows changes in gandhara and dhaivata after the removal of the additonal rishabha.
7.Ghanta indicates addition of Rishabha and dhaivatha with change in gandhara.
8.The last change is extremely complex.It basically indicates addition of gandhara and nishadha.

Dikshitar's mastery can be seen if we use Todi as the base.Then we find this analysis.
- On two occasions in successive songs he has changed only one swara.
- On three occasions he has changed two swaras
- On four occasions he has changed three swaras

c.The swara-sequential changes  has been pendulous especially after the thrid navavarana.

d.We have one raga with two nishada swaras
- we have one raga with two dhaivata swaras
- we have one raga with two rishabha swaras
- we have one raga with two  rishabha  and two dhaivatha swaras
- we have one raga with two rishabha , two gandhara , two dhaivatha and two nishada swaras.
Dikshitar excelled by choosin dwiswara ragas.Musical genius apart this is indicative of the shiva-shakti bindu concept and the preponderance of dwiswara ragas is a natural and brilliant choice.

e.The switch-over from Kalyani to Shankarabaranam is   master-stroke.Kalyani is said to be the mirror-image of Shankarabharanam, caused by the change of  Madhyama.Remember the reference to the sun being reflected by the mirror in the shrividya passage? Dikshitar came to the object from the mirror image.Once having come you dont go back to reflections or images again.Hence , no more prati-madhyama ragas were used - a masterstroke indeed.

f.He has used one nishadantya raga - usually sung in madhyama sruti.

g.He has used two ubhaya vakra ragas.He has used one traivakra raga.

h.He has used one chaayaalaka raaga - ghanta which has nuances of both bhairavi and dhanyashi.

i.He has used only four chakras - veda,netra, bana and rudra.This corresponds to the four groups in the shrichakra - square, circular, triangular and spot ( chaturanga, vyuha,ara or kona and bindu) .

It is amply clear that Dikshitar adopted a scheme in his choice , duly infusing siginificant musicological content in his choice.

[Extracts from the monograph released by the RK Shrikantan trust ]