Spent a large number of "deployments" to ELF-1 back in the 90's (ended up with a short tour, which caused a bit of a kerfluffle due to no SOFA at the time). Drove by/through USMTM quite a bit. Had some friends stationed there as well. Found a few interesting shops in the city back in the day, but the better ones were in Abu Dhabi or now, from what I hear, Dubai. (
http://www.padi.com/scuba/scuba-diving-trips/scuba-diving-resort-vacations/United-Arab-Emirates/) and (
http://www.scubaboard.com/forums/the-gulf/61922-diving-persian-arabian-gulf.html) If you can hit the coast there are some nice *warmer than normal* reefs in the Arabian Gulf to snorkel/dive over. They do have some good populations of sea snakes, so keep an eye or two out for unwanted company and hit the water with someone that's been in that area for a while. It would be great if you could do some documentation of temps, SG, and wildlife - I know nearly all of us on this site would be interested.
Bahrain is interesting and a few hour drive (desolation boulevard - the highway between Riyadh and Bahrain is long, straight, and barren, with the landscape only broken up by the occasional "oasis" gas station or scarring from tanker wrecks). Warmer water still, but still interesting.
Look up Tridacnids from the region as well - there are some interesting recent developments (newly discovered/rediscovered) that might make it worthwhile to pick up a camera capable of taking underwater photos.
Hope this helps in your adventures.
Oh, one other note. It does get, er, "warm" in Riyadh, but it's a good idea to get used to wearing long sleeve shirts and long pants and a hat in the heat nonetheless - keep the sun off. And the Ring-neck Parakeet hang in and travel through the area to hit Jabal AlAhkdar in Oman (the green mountains) on the Eastern end of the peninsula. Hit Google for some good images from the region. If I would have had the time, I would happily have taken a trip there.
Hope this helps in your adventures, man.
Ray