If Anatolian did not go too far from Proto-Indo-European, Hitto-Luwian made a larger progress. First of all, it suffered great influence from the aboriginal non-Indo-European tribes of Asia Minor, Northern Syria and Armenia. Religious beliefs, land and economy terms, personal names and place names were borrowed from Hatti and other nations of this region. It was reflected also in the structure of the language.
The Hitto-Luwian phonetics changed greatly comparing to Proto-Indo-European. Only 5 vowels remained in use (a, e, u, i and nasal e). This was caused by complete assimilation of long and short o, long and short a nad Indo-European "schwa" (@) by Hitto-Luwian a, etc. The number of diphthongs also was reduced, though syllable vowels remained as they were. Consonants lost voiced aspirants (*bh, *gh, *dh), but labiovelars and unvoiced aspirants were preserved.
The loss or change of the noun and verbal endings continued here. It is necessary to notice that Hitto-Luwian was the only Indo-European language which had nine cases of nouns. The special case ending was used for the so-called "directional case", which disappeared in both Hittite and Luwian. Genitive had tow different forms, for animate and unanimate nouns. This together with the gender system (two of them: common and neuter) makes us think Hitto-Luwian did not develop directly from Proto-Indo-European, but exactly from Common Anatolian with its archaic structure.
Hitto-Luwian dictionary consisted of about 30-40% Indo-European words, the rest were already borrowings. In Hittite, Luwian and Palaic, this percentage decreased even more.