I bought a new GS150 about 5 months ago (ran ~4500km till now). Here are some problems and observations I've come across:
One side mirror caught rust in the first month.
Very poor rear brake shoe. Already replaced twice within 3000kms. (Rs.350)
Rear brake light switch replaced once (Rs.70). I get my bike washed twice a month at least and this switch is exposed so thats probably why it stopped working.
Headlight bulb replaced once due to high beam not working. Again due to water from wash.
Bike did missing but was reduced after some running and fixed after first tuning.
Quality wise the bike is average. Not good but not that bad as some people say. It reqiures some care from your side. Parts are cheap and easily available. Engine wise the bike is seriously good. My bike reaches 100 km/h instantly without vibration without me noticing. Ride is very comfortable as well. Seat was very hard when it was new and still is somewhat. So if you have daily commute of 80-90km, then you should change or modify the seat. Average of my bike is ~45km/liter so its very good.
Also, I would urge you to seriously reconsider GD110S. Its better in almost every way than GS150. And don't be fooled by 110cc vs 150cc. It can easily keep up with GS150 in speed.