NCl Spirit is an old ship: common areas are well maintained but staterooms show their age. So, unless this is the very first cruise ship you see in your life, the impact with this ship is a little disappointing.
The atmospehere is very relaxed and "familiar". This was my 3rd cruise with NCL and I appreciated the freestyle cruising aboard the Spirit more than with Gem and Jade.
The staff was not intrusive and we never felt compelled to buy drinks or bingo cards or anything else that we did not want to buy.