I've only played a couple games of relic so i don't really have the game mode fully figured out yet, but the shield just seems quite weak. I saw a lot of them laying around, I think people (including myself) were just dropping them rather than use them, because guns are more useful.
The shield is too weak and slow to close any gaps, the lunge on the melee is too short, etc. I just couldn't find any way to make a play with the shield. Hopefully as they continue to tweak it they can give the shield a niche.