The Istana is a reasonable hotel - but don't expect it to be the five star standard as it really is quite old and dated. The carpets are generally dirty as are the bathroom areas and the whole hotel is really in need of an upgrade and refurbishment. However, it is in a good location and is generally well priced. The swimming pool is reasonable. While we were there our room became filled with fumes - we all ended up with a headache. When we complained we were told the room next door was being repainted and we were moved to a different room. The way it was handled wasn't very good, no apologies made and it took two hours to sort out the change. In decor and condition, the room moved to was far worse and the carpets were threadbare.
So all in all, yes it is worth staying at as long as you are aware that the quality etc is not going to be terrific and problems are not handled well.
The breakfast is very very nice with a wide range of choices and the chefs will cook things freshly for you as well.