What sound features distinguish Indo-Aryan languages from most other Indo-European languages?

The sound features that most clearly distinguish Indo-Aryan languages from the majority of other Indo-European languages are the presence of voiced aspirate stops and retroflex consonants.1

• Voiced Aspirate Stops: These sounds (such as gh, jh, dh, and bh) are produced with an accompanying audible puff of breath. While these are a defining characteristic of the language family, some outlying modern languages have lost them due to external linguistic influences; for example, Kashmiri lacks voiced aspirates, and Sinhalese has no aspirated stops at all.1
• Retroflex Consonants: These are sounds produced by curling the tip of the tongue upward toward the hard palate. The proliferation of these sounds in Indo-Aryan is widely attributed to the influence of Dravidian languages, which possess a similar phonological feature. Similar to the aspirates, some modern Indo-Aryan languages have lost these sounds, such as Assamese.213