Some of the north-eastern NITs are excellent in terms of quality of education and facilities offered such as NIT Silchar, and NIT Agartala. Academics at these NITs can be compared to old NITs such as Durgapur, Kurukshetra, and Raipur.
The rest of the north-eastern NITs are still in the developing period and ranked below the old NITs.
Most people will tell you that old and established institutes will always have more to offer as compared to newer established institutes. You will have advantages in terms of reputation, more clubs, better campus, alumni as most new NITs will operate from a temporary campus.
Since you are particularly asking about North-East NITs, you can divide them into two categories:
Old NITs: NIT Silchar and NIT Agartala are two universities that fall in this category. They have a good campus, active clubs and cells, decent placements, and infrastructure too. These two are better than most new NITs even in the mainland and some other older ones as well.
New NITs: All other NITs will fall under this category from the northeast. Meghalaya, Sikkim, Arunachal Pradesh, Mizoram, Nagaland are included here. All of them are new institutes and most of them will have their own set of issues that most new institutes face. But, you will get the promise of being in an NIT. Additionally, the best part is that you will have a peer group no matter which NIT you get into as all have cracked the JEE Mains to be here.
Every NIT and IIT has a success story but they will not reveal their failures. It ultimately boils down to your hard work and determination which will determine your story.