Dreadmorph Ogre; I agree rating 4 (out of 5). It's one of the top half dozen beatstiks in the game. With a spawn cost of 11 you can't afford more than one in the warband unless you have at least one unit with energise (e.g. HeartsBlood Temple) But it is good enough that it's worth considering using the temple to spawn multiple Dreadmorphs.

Fleshless Reaper; I'd rate it as a 3 going on 5. It's Very Good at denying the center cell to your opponent. Sufficiently good that it might deserve a (5) But because it cannot attack (power-0) it's crippling to play more than one, hence the (3) part of it's rating.

Falcon Soldier; Valor has multiple choices of creatures which are better for this spawn cost {Knight of Sorrow, Twilight Scout, Scarab warcharm.}  Even in a pure Valor warband, you won't run out of better options to include. So I'd rate it a 1.

Note; The only rare I'd rate as unconditionally (5) is the scarab warcharm. There are several commons I'd rate as a (5) {Jack-of-blades, Cannibal pariah, Faceless Stalker, Inspired Samurai etc) But the Scarab is the only rare.