After some testing, and some seriously mean strategic use of capture locks and teleports, I've come to the conclusion that health crystals in the middle of the map are not conducive to fair play. There are two maps that have these: Manadala and Exile. I'll look at each seperately as the severity of the issue is drastically different on each map. However, the primary issue with 'unfair play' using these crystals is that they favour heavy hitters (Rook, Unclean Beast, Torch Bearer) and unfortunately players are not at liberty to choose which map they are placed upon before selecting a character.
Situated in the middle of the map is a health crystal that is close enough to the enemy towers guarding the +30% health and damage flag for each team, to attack, return to heal, and attack again and eventually steal this flag. The issue with this placement is that it can be nigh impossible to uproot certain demigods from this location due to the easy access to recover health/mana and nearby towers for retreat if the flag is stolen. The factor that was intended to serve to balance the location is that is it not on any creep lanes, and 'camping' in this location can have negative side effects in the form of lost xp, through the gold gained in destroying the enemy's towers can often make up for this. Personally I dislike the idea of a strategic map point benefiting certain demigods more than others and would prefer this to be changed to a gold mine and/or artifact shop instead.
Situated on either side of the map are two health crystals, each one closer to one team than the other. Both of the flags controlling these crystals have different benefits, the one closest to the dark side provides +15 mana/sec, the one closest to the light side provides +15 health/sec. Both of these crystals are next to creep lanes, meaning there is no strategic disadvantage to holding these locations, and as previously discussed contain more benefit to some demigods than others. The biggest issue here is how heavily loaded these locations are and holding them both will often spell game, but an additional concern is that they are not inherently equal: +15 mana/sec > +15 health/sec. This is especially true for demigods that can transform mana into health (Rook, Sedna, QoT, Erebus), but is true for all demigods in the form of spike damage trumping health regen. I'm going to petition that the health crystals be removed from these locations and the flags provide a benefit other than increased mana and health regen (or that they both provide the same type).
There may be a secondary issue here with the mana regen flag though, as it nearly completely negates the requirement to purchase gear that improves mana regeneration for half of the demigods (Rook, Regulus, Unclean Beast, Oak), and making an adjustment to the ammount it provides (+7?) might help to rebalance this with other flag types.
If you have any arguments with the above, please post.