Hi hmronnow,
you are right that is a good idea to visit the schools, several times if possible, as it is only by seeing a school in action that you will get an intuitive feel about whether it is the right place for your child to learn and be happy.
I can give you some general observations on the two schools, as I agree that on paper they do look similar in terms of the curriculum that they teach. I keep my thoughts factual as choosing a school is a very personal decision, and as I always say to parents, there is no "best school" but there is certainly the best school choice for your child.
Firstly, both schools are true IB schools meaning that they follow the IBO curriculum from start to finish, so from this point of view they are very similar. More details about the curriculum here http://www.ibo.org/programmes/primar...me/curriculum/
The foundations of the schools are very different. At ISL they are a not for profit foundation, set up to educate the children of expats moving to the area. They have special agreements in place with a number of employers and usually have a waiting list for places. At GEMS the school was founded in 2013, so is a new school and is still building up the number of students. It is also a for profit school, part of a global chain of school, over 70 I think, in the middle east, asia and all over the world. An important question for you is which kind of approach to education you prefer? It is important as it does make a big difference in the way a school is run.
The length of time a school is established also makes a difference to the education offered. In a newer school you are likely to get smaller classes and higher teacher:student ratios as the classes are not yet full. Yet in an established school, it has had a chance to bed down, build a senior management and teaching team that are loyal to the school. The character of a school also takes time to build.
The situation of the schools is also very different, ISL a more countryside campus and GEMS is off the motorway in a more industrial zone. That being said there is a lot at GEMS to compensate for its position. From a facilities point of view it is really incredible and no school can match it, but ISL facilities are also way above average, even if not in quite the same league.
Another school in the area that follows the IB programme in the senior school and is soon to introduce the Matu is La Cote School. Very different to both schools you have mentioned in your post so worth visiting if it is in the right location for you.
If you have any specific questions, feel free to PM me.
Good luck!