They are well-established in the UK - you can see their website here http://www.acs-schools.com/acs-doha.aspx

I have toured the campus and have to say it's quite impressive. My son is at Compass, which I am quite happy with, but you won't go wrong with ACS-Doha either.

Here's some info from their website:

The Programme

Initially we will be offering our prestigious Early Years, Lower School, and Middle School curriculums, based on globally recognised American and international standards, with an aim to deliver the same range of academic programmes successfully offered at our three UK campuses [learn more]. As the campus develops a High School we will also seek authorisation to offer prestigious US College Board Advanced Placement (AP) courses. ACS Doha will also offer an American High School Honours Diploma. The school will shortly be a member of the Council of International Schools.

The Doha campus offers a rigorous academic curriculum of English, mathematics, science, humanities, world languages, and fine arts. Our programme challenges students to become independent, reflective, inquiring, and knowledgeable; confident communicators who are principled, open-minded and caring; socially and emotionally intelligent and able to embrace the importance of a healthy and balanced lifestyle.