I've personally had no issues with the service provided by GgStore!
I ordered Tetris Effect recently and although there was some delay in getting it (and this was simply because they didn't have it in stock and thus I had to order it) once I got it I couldn't be more happy! I got a fantastic game, for a fantastic value, and really it only took around two weeks to receive anyway which is nothing (considering I usually order from overseas and sometimes it can take a couple months).
GgStore has an interesting business model. The have a system which automatically seeks the lowest retail sale, and then they lower the price based on that - so you're almost guaranteed to get the BEST deal possible! Of course, since the system is automated sometimes things go wrong and an order can't proceed or it takes longer than anticipated: but this is a risk you should be willing to take, as there's really no loss as you'll receive a full refund.
So okay, the pros;
*Guaranteed the best deal for a brand new game if you do a little research before hand.
*Usually two weeks delivery if an item is on 'order' or possible less than a week if they have the item in stock already.
*Fully refunded if something goes amiss.
*There are GenoaPay and LayBuy options for added convenience for any order regardless of value (I think).
And the cons;
*You're not guaranteed to receive a product you ordered due to how their system works.
*Shipping can be delayed depending on how long it takes the seller to get the product if it was on order.
Really, the pros out-weigh the cons and as such I really recommend GgStore if you're okay that there could be a chance your order doesn't go through. So maybe do it for a game you'd like but aren't super hyping over and are fine with forgetting about until you receive a surprise in the mail.
I gave 4 stars instead of 5 simply because I have had one time where an order was cancelled. So yeah, minus one star because of inconvenience.