I booked ISIS in Siam Square to have a cheapish place to stay for the first 2 nights after a long flight.
I think that was a mistake for me, since the hotel is very noisy. First of all, it is located right at a very busy street and there was all kinds of noise going on early (6am), construction, traffic, loudspeaker events.
The hotel itself was also very noisy. Doors keep no sound out, so if you get a room next to the elevator, you'll hear that loud announcing sound many times during the day. Guests where also VERY loud. Some poorly behaved families with kids shouted in the hallways for a long time in the mornings. People this poorly behaved shouldn't travel.
The hotel seems rather old. It shows in having electricity outlets that are not near the bed, thus not suitable for laptop/phone use. TV is very small.
On the positive side is the friendly staff and an excellent breakfast buffet, despite being slightly expensive (400THB+). It also on paper has a good location, right on the BTS, just be aware it is extremely trafficked, maybe the most trafficked in all of Bangkok.
Overall, I will not recommend this if you're looking for comfort and peace. Maybe as a place for families with kids, since they're allowed to scream and shout in the hallways.