I have always thought that GSMarena reviews are a bit late compared to some major blogs. Though like vlad0 said, Lumia 1020 is only out for AT&T and no Euro version is yet selling anywhere.
Their review is really the only one I care. I have usually researched the device before it comes out so that I know everything generic that the likes of Engadget, The Verge etc will mention.
Where GSMArena shines is the very detailed sound quality via 3.5mm jack review, proper battery test and camera review. All things that pretty much no other site reviews properly, especially the sound quality part.