War in the North, Shadow of Mordor, and other non-canonical Middle Earth stories are not that bad.
Shadow of Mordor does not alter any writings of Tolkien, so no lore is broken. The added lore should not be considered canonical, however, it provides explanations or details not written.
For instance, War in the North features a Dwarven city called "Nordinbad". When Erebor fell, the dwarves were scattered. it was never written "every Dwarf went to the Blue Mountains" so there is a high chance many strongholds in the mountains were built.
non-canonical lore should not be avoided, unless it changes something written. adding things is not changing things.