I've travelled twice with Garuda Indonesia for international flights so far, and it is a good airline.
The planes were modern and clean. Seating in Economy Class was decent and not as tight as in other airlines.
My last flight with them was comfortable and punctual. The entertainment program was decent, but not as good as that offered by other international airlines for similar distances, and not as as good as Qantas Domestic for long flights.
In my last flight, only five and a half hours long, they provided travellers with a snack at night and a full breakfast in the morning. Food was all right regarding taste and variety.
The flight attendants were lovely both in the airport and on the plane, but the in-flight communications in English were a pain to listen to.
In short, a good airline to fly with, but nothing one would be looking forward to unless the ticket includes a part of the route with them.