Spirit is a good choice if you havent cruised before, or if you are a little bewildered by all these super-dooper-mega-sized ships, in a nut-shell, she is smaller than many and a few years old, but ex HAL so good up-keep, celebration will be on par as also ex HAL, not sure about destiny, slightly bigger, but ex airtours so will have all of her old passengers on, and emerald ok, lots of die hards but a bit more traditional in style.
Spirit will give you excellent attentive service, more personal than bigger mass-market ships, still enough space to chill, very nice food - dont be put off by price, is better than some of major cruise lines, not so strict, dress up if you want, buffet every day if you want type thing. Cabins nice, not completely refurbished but ok.
Good itineraries for 05, even better for red sea in winter!
I say go for it, better than airtours were, and a hundred times better than island escape.
Pre-book the drinks package would be my top tip!
Have a great holiday