Based on the pictures its a low end bike shop quality mountain bike. My guess is that it was made between 1985 and 1995.
For reference, in my mind there are two main categories of bicycle:
- Bike shop bikes
- Department store bikes
As a general rule (and there are exceptions) any bike shop bike is better than the best department store bike.
The long wheelbase will offer a smooth, stable ride. The bike is good for street and light trail riding. The bike looks like it has not been ridden very much and it can provide you with many years of service.
The two main things are:
- Does this bike match the kind of riding you want to do?
- Does this bike fit you?
From a fit perspective I'd go with generic "stand over" sizing. Stand over the top tube of the frame - for street riding about 1" of clearance is fine. For more aggressive trail riding more clearance is needed.
If you decide you will be riding on road or smooth trails you could consider replacing the knobby tires with smoother, street tires for a smoother ride and reduced rolling resistance.