"Col de la Croix de Cœur 2174m CH-VS-2173 (R1)
Trying to find the road to Col des Gentianes (there is no road to this
pass really -- it is a path and then a ski piste (S2-3 in my opinion))
2350m (lost my way and walked around the grassy hills and anyway had
some nice views)"
There is a gravel road to Col des Gentianes and it is in very good shape.
For gravel roads you should check the Swiss topo map here:
http://map.veloland.ch/?lang=en&p&route=allThis map is very detailed and usually up-to-date. I never found better topo map in any swiss shop, so I always print this one and take with me :-)
The road to Gentianes is very attractive - the top sections goes very close to glaciers. I cycled it in the summer 2008. The top is at 2904-2908 m a.s.l. because the ski resort is located little higher than the geographical pass. The climb is much easier than Col du Jandri. Maximum gradients are about 15-18%. The other side of Col des Gentianes is a stony path (uncyclable even with full suspension bike).
Very close to Col des Gentianes is another nice climb - Les Attelas. It is 200 m lower but very hard, with several 30% ramps. The view from the top is outstanding, during sunny weather you will be able to see the biggest group of 4000 peaks in the Alps.
It is possible to include Croix de Coeur (2173 m), Les Attelas (2733 m) + Col de Chassoure (2744 m) and Col des Gentianes (2904 m) in one day, because these roads connects each other at Les Ruinettes (2192 m).