A couple more things I'd like to add - please correct me if I'm wrong (I'm a listener, not a practitioner).
One important thing about rāgas that differentiates them from western modes is that they typically come with notions of note ordering. That is, when playing an ascending melody, you may be encouraged to pick different notes than for a descending one. There are a couple of western modes that work in a similar way, but typically only for a single note, and these modes are not widely used.
Another distinction is that while rāgas are like western modes in that they are culturally identified with emotional states, in ICM the emotional states are generally thought of as temporal (time of day, time of year). One does not think of a particular rāga as "sad" or "happy", but rather (for example) associated with sunrise, or twilight, or the deepest part of winter.
Finally, it is important to note that harmony plays very little role in ICM, which has instead developed its ideas regarding melody to a degree substantially beyond western classical music (which has focused a great deal of effort on advancing the concepts and use of harmony). Listening to ICM live with an experienced audience, you may hear gasps as the lead performer swoops up and down melodic lines, in ways that you would never encounter in a western context. For ICM listeners, the choice to play three particular notes one after the other can be a source of intense joy (or, occasionally, intense irritation).
I am hope I am writing about these aspects correctly.
> you may be encouraged to pick different notes than for a descending one
Hmm, this is not entirely true. There are absolutely symmetric rāgas, and some of these are extremely popular: I mentioned Śankarābharaṇaṃ, but there are several others, like Kalyani (Lydian mode), Tōdi (Phrygian mode), or pentatonic scales like Mohanam, Hamsadhwani, Hindōḷaṃ, etc.
> in ICM the emotional states are generally thought of as temporal
Indeed. One might think minor scales are 'more sad' than major ones, but this doesn't translate well to Indian classical music.
> it is important to note that harmony plays very little role in ICM
Also true. Indian classical music has little theoretical and practical use of 'chords' in the Western sense, except perhaps the drone strings on the vīṇā.
One important thing about rāgas that differentiates them from western modes is that they typically come with notions of note ordering. That is, when playing an ascending melody, you may be encouraged to pick different notes than for a descending one. There are a couple of western modes that work in a similar way, but typically only for a single note, and these modes are not widely used.
Another distinction is that while rāgas are like western modes in that they are culturally identified with emotional states, in ICM the emotional states are generally thought of as temporal (time of day, time of year). One does not think of a particular rāga as "sad" or "happy", but rather (for example) associated with sunrise, or twilight, or the deepest part of winter.
Finally, it is important to note that harmony plays very little role in ICM, which has instead developed its ideas regarding melody to a degree substantially beyond western classical music (which has focused a great deal of effort on advancing the concepts and use of harmony). Listening to ICM live with an experienced audience, you may hear gasps as the lead performer swoops up and down melodic lines, in ways that you would never encounter in a western context. For ICM listeners, the choice to play three particular notes one after the other can be a source of intense joy (or, occasionally, intense irritation).
I am hope I am writing about these aspects correctly.