Shadowmoor really had some awesome cards, didn't it?
Normally, lifegain isn't that powerful, but this card makes most lifegain effects viable. The only real problem with this card (and most of the other other Reflections) is that it costs too much. WotC recently recified this mistake by printing Rhox Faithmender, although as a creature, it can die easier (but that's for a later review).
Pros: Double all your lifegain
When a lot of people read this card, they think "oh, all of my opponent's lands tap for double now". While technically true, people often forget that things like Sachi, Daughter of Seshiro and Manalith are also affected. People didn't see this as a problem in my Sachi EDH until I started jumping from 16 mana a turn to 50 mana a turn. Great card and well-priced for it's effect, albeit it's double-green requirement may make it a little difficult to splash.
Pros: Doubles mana production of all your permanents
If this doesn't make your field scary, nothing will. Giving one thing double strike is usually scary enough, but giving an entire board double strike is terrifying. Red can't really ramp up to the 6 mana required easily, but it can burst the mana using rituals so it's at an achievable level. The cost is well-deserving of the effect for sure.
Pros: Makes an entire field extremely threatening
Cons: Costs 6 in red, double-red
This is my least-favourite Reflection. Yes, it's ability is powerful, especially in blue. However, it also has the titles of "most expensive" and "most colour-intesive" as well, which are anchors to its greatness. Blue is probably the colour with the most difficulty in mana ramping, so making this cost 7 is fairly out of the average deck's reach. With it being so colour-intensive, it makes it hard to put in a colour like green or white in order to get that mana-production that you need to play this. It has great potential, it just costs a tad too much.
Pros: Doubles each draw
Cons: Costs 7, triple-blue
There's nothing like hitting someone with a Sorin's Vengeance with this card out. I love two things about this card especially. First, it specifies that the life loss occurs at the end of each turn (as opposed to on that player's turn only), so any life lost on your turn is double. I also love how it affects each opponent (as opposed to just one), which means that your Armageddon Clock rings that much louder for everyone except you. Finally, it only costs 6, which is great for what it does, as well as only one black mana, which makes it very usable in b/r or Jund decks.
Pros: Doubles life loss for all opponents, happens every turn