In reply to Stephen James:
There's a lot of info on the East Arete of Glyder Fawr in the UKC logbook. Most people agree the rock is loose, gear is poor and belays hard to summon amongst the grass and choss. So, probably quite adventurous and interesting at the grade.
Central Arete I have climbed and I remember it as a scramble first pitch followed by a long pitch of surprisingly tenuous climbing on snappy holds with sparse and sometimes poor gear... for the grade. Above this, it becomes a fun jenga-tower and ridge. I'd pick this over EA.
If you've not done loads in Cwm Idwal, I'd recommend instead linking the Slabs into Holly Tree Wall, the Continuation Wall and then Cneifion Arete. If it's late, head down for a dip and dinner. If it's only, say, 2pm, you could then try a route on Glyder Fach or the East Face of Tryfan.
Hope that helps.