Went last year, probably going back this summer - awesome crag.
We stayed in an excellent campsite in Yenne, about 10mins away.
http://www.eurocampings.co.uk/en/europe/france/rhone-alpes/savoie/camping-des-lacs-117541/Some basic info and topos:
http://www.camptocamp.org/sites/109791/fr/la-balme-de-yennehttp://planetgrimpe.com/Topo/BalmedeYenne.pdfFor warm-ups/easier routes there's a section (not on the topo) on the other side of some trees at the far left side of the crag, about 6-8 routes.
The crag faces north and is heavily tufa-rated, according to the locals we were quite lucky to find it dry - so might be worth checking if there's been a wet Spring.
Most of the in-situ gear is Ok but there's a couple of dangerously worn draws - take a couple of QD's even if your route looks equipped. Some of the routes can be a little 'sporting' but most are bolted well.
Recommendations: everything, but of the stuff I did:
All the warm-ups were worth doing
Colonnette 7a
Alien L1 7c+
Berhault 7b+
King Kong 7c+ (fell off on the flash but what I did was excellent and the rest looked better)
Cathedral 7b+ didn't try this but it's supposed to be one of the classics of the crag.
There's another crag a short drive away, I'm trying to remember the name, which was mostly vertical 6's which maybe a rest day option.