As of writing this, I have placed nearly 50 orders through CDJ with no major issues to note. They've always been quick to reply to any emails about orders and also let me know as soon as there are any changes due to supply status, release changes, etc... The only issue I've ever had was due to the manufacturer making the package extremely large, thus drastically changing the shipping charge. CDJ emailed me about the issue along with the new amount and gave me the option to continue or cancel the order because of the increase.
CDJapan has always had the best prices for the items I've been looking for (CDs, BDs, books, and figures). There are about 4 shops from Japan I use for shopping, but CDJ has always been my go-to choice.
They also typically offer 3-5 different shipping options covering low-price surface travel, mid-price 1-2 week EMS, and 3-5 day FedEx/DHL. Options to fit everyone's budget and needs.