It will be gross.

It won't have enough fat to be the binder/stiffner you need for a successful cheesecake.

It will be a messy eye sore flop when you go to cut into it and serve on a plate (top with whip cream to minimize how deflated it looks).

Add butter?

I wouldn't do that and I've made a lot of cheesecakes. Sorry, I know going to the store again blows but it is your best bet.

I always use light and my cheesecakes turn out fine.

Regular will work better and taste better. The light ones have extra ingredients and do not break down and mix together as well as the regular ones.

Does this really make a big difference? Asking genuinely as an avid home cook but not so much a baker. I am trying a new cheesecake, which admittedly I don’t make often, and planned to use 1 package regular cream cheese and 1 neufchatel thinking it won’t be too noticeable at half.

Am I much mistaken?

Honestly I don’t think so. I would try another store or two.

It'll do, it may bit taste as good. Maybe add an extra egg?

Went to two stores this morning and none had regular cream cheese in stock. I bought three sticks of 1/3 reduced fat Philadelphia cream cheese for a pumpkin cheesecake. Wil this work?