Dominions are pretty much Sisters of Battle with the Scout USR, now to most this doesn't seem tempting scout isn't really worth the extra points, but it isn't the Dominions themselves that are deadly but how they combine their wargear and special rules. Dominions can take 2 Special Weapons per 5 Sisters, the weapons up for grabs are a Storm Bolter, Meltagun or Flamer. No one ever chooses the Storm Bolter but a unit that can Outflank 4 Meltaguns and with a good BS is great, this is the same for the Flamers, its a effective way for causing panic in the back lines. Dominions are pretty much a suicide unit, Outflank then kill something before your wiped off the board, but we cannot forget these girls wear Power Armour meaning the have a chance of survival, though its slim since most of the enemies fire will be directed at them.
Special rules are pretty blank, the standard Sisters rules and Scout. Their Act of Faith is Holy Fusillade and it is amazing, making all weapons the Dominions carry Twin-Linked, making Meltaguns accurate and Flamers Re-roll to wound, this usually means when Dominions hit they hit hard.
This review was kind of small, so with that I'll give you a few ways I play Dominions. I tend to play a Flamer Dominion Squad in an Immolator, this gives me a horrid Twin-Linked Heavy Flamer from the Immolator and 3 Flamers (the Sister Superior has a Combi-Flamer) from the Dominions this usually gives me they upper hand as they Outflank and torch any unit they can. Alternatively I have played this strategy with an all Melta squad too, the thing to remember with Dominions is they suck at being take all comers, yeah you can have a Meltagun and Flamer, but neither will be as effective, Dominions have to be specialized.
My verdict on Dominions are still they same, these girls stand out as being handy and quite powerful, whilst one sided, they do their job well and like the Seraphim fill that effective aggressive role that is so desperately needs to be filled, Sure Repentia are aggressive but not reliable. They are a relatively good unit all in all, but not the best.