With four sets of Magic being released each year it seems like there's very little downtime between the guessing and excitement that comes with each release—this is probably intentional. At the same time with the increasing number of highly visible Constructed tournaments being held each week formats are solved much faster now than ever before and each set provides a breath of fresh air for players who are tired of the same old strategies. If anything it might be the case that new cards are not released frequently enough to "shake up" Constructed metagames.
But I digress.
There are some very interesting new cards in M13 several of which have the potential to impact Constructed (at least for this article we're ignoring reprints even the really really good ones like Rancor). We have a vested interest in identifying these cards to get a hold of them at reduced prices. Remember when Blade Splicer debuted at 99 cents and Bonfire of the Damned was a pseudo bulk mythic for a few days?
The first card that might catch our interest is Cathedral of War.
As a colorless comes-into-play-tapped land Cathedral's ability needs to be very very strong in order for it to see Constructed play. The advantage of many utility lands is that they do not occupy a "spell" slot in a deck but rather occupy a land slot with a minor downside (see especially dual-colored manlands like Raging Ravine). The worse the "land part" of the card gets the less honestly we can say that it occupies a land slot in a deck. Is a colorless comes-into-play-tapped land even a land? Barely.
Unless there is an exalted deck with incredible fixing or a solid mana base it is unlikely that a full set of Cathedral of War will be included in a deck as an opening hand with multiple Cathedrals will often be unplayable. That having been said there is certainly room for one or two copies in decks that can use the exalted mechanic and it is conceivable that some sort of white-based exalted deck will exist in which case Cathedral of War might actually increase in value. For now it seems reasonable to obtain a few copies but a full playset probably isn't necessary.
The next card Thragtusk is difficult to evaluate.
Right now U/W decks have largely have pushed Wolf Run Ramp out of the metagame making midrange strategies viable. Thragtusk is almost the epitome of a midrange card. It's a reasonably sized beater (five power for five mana) with considerable upsides: five life and a 3/3 token. It's not a super-aggressive card nor is it a control powerhouse (although it probably would go very well in a G/W Control deck were one to emerge).
Paired with cards like Cloudshift or more relevantly Restoration Angel Thragtusk generates a ton of value. When I was looking at this card a couple weeks ago I figured that if cards were banned from U/W Delver that this card would have to wait until the Titans rotate in the fall to unleash its full potential. Since nothing ended up getting banned from U/W Delver I expect Thragtusk to become a role-player in Standard.
What about Mwonvuli Beast Tracker?
As a 2/1 for 1GG its ability has to be pretty strong for it to see play (see: Eternal Witness). At first glance this card doesn't seem very good. The types of things for which it can Tutor are relatively limited it doesn't actually generate card advantage and there is always the risk of a rogue Thought Scour completely nullifying the card.
However if a Bant Hexproof deck ever makes waves in the metagame Mwonvuli Beast Tracker may be used to fetch Geist of Saint Traft or even Invisible Stalker. This is a very limited application but for this reason alone it may be a card to watch. It also has potential as a one-of in Wolf Run Ramp (there may be times when for mana considerations it would be better to Green Sun's Zenith for Mwonvuli Beast Tracker rather than wait to hit seven mana to directly get a Primeval Titan).
Then we get to Talrand Sky Summoner.
At first I thought that this card was simply too clunky to be of any use. The standard of what we get from a creature for four mana has increased dramatically in recent years and a 2/2 rarely makes the cut. However if the metagame continues to favor U/W Delver and midrange-style decks then this might actually be an amazing sideboard card. As terrible as Talrand is against cards like Huntmaster of the Fells and Bonfire of the Damned resolving him against a Delver deck seems pretty good. There is the potential for immediate returns via Gitaxian Probe and untapping with this card in play nearly guarantees free Wind Drakes each of which can block and kill a flipped Delver of Secrets.
But there is the possibility that Jace's Phantasm will play a role in U/W decks as well.
Flying Men always has been a "reasonable" card and the fact that Jace's Phantasm flies immediately rather than needing to resolve a specific trigger is a point in its favor (compared to Delver). However short of running clunky cards alongside it (i.e. Mind Sculpt) which we shouldn't do it isn't likely to become a 5/5 in the early game. Delver of Secrets is an especially strong card because it can "blind" flip on turn 2 and attack for three immediately and it is very likely to flip on turn 3 following a Ponder.
While attacking for one isn't the worst thing in the world Jace's Phantasm simply isn't as aggressive as Delver of Secrets because it will never "flip" on the first several turns. At the same time however in a protracted mirror match it's a much better card to draw off of the top than Delver. It's an especially spicy card if decks continue to reduce the number of copies of Moorland Haunt that they run as many recent contenders have. It also does a reasonable job of carrying a Sword and for a short amount of time it may increase the value of Sword of Body and Mind over other pieces of equipment.
The most obvious two-card comparison is between Sublime Archangel and Rafiq of the Many—both are heavy-hitting exalted cards at 4CC. When each is the only creature in play Sublime Archangel has the edge in terms of evasion but "only" attacks for five whereas Rafiq attacks for eight but is much easier to block. In terms of involving other creatures in combat (i.e. Invisible Stalker Geist of Saint Traft etc.) Rafiq of the Many is the better card in terms of exalted combat when the number of creatures we control is less than the attacking creature's power plus two.
It's a misleading comparison in some ways though because there isn't a choice between the two: it's Sublime Archangel or nothing. However comparing the card to Rafiq is a good way to assess her power level. Further Sublime Archangel is not legendary so there can be multiple instances of exalted on each creature we control and it's not the case that we need to use exalted—the Angel is still a 4/3 flyer for four and we can do an "old fashioned" and just attack with some Spirits and bigger fliers.
Finally we have Ajani Caller of the Pride.
Although we've seen a very underpowered 2CC planeswalker we never have seen an unplayable 3CC planeswalker (Jace Beleren and Liliana of the Veil). Despite his cost though Ajani is a card that becomes more powerful after turn 2. Yes it is possible to play Birds of Paradise into Ajani for a counter (and that puts us further toward resolving his very powerful ultimate ability) but dropping counters onto Birds of Paradise or Avacyn's Pilgrim isn't very effective. We want to be able to increase the combat resilience of cards like Geist of Saint Traft and Delver of Secrets.
Further if an exalted-themed deck emerges his ability will be much more effective than it seems. His second ability is very limited in scope (Elspeth Knight-Errant does something comparable for +1 rather than -3) but may also play nicely with a Sworded/exalted creature. While he doesn't provide a Glorious Anthem effect like Ajani Goldmane the new Ajani actually seems like a decent card though perhaps not quite worth his current price tag.
Despite 170 cards in M13 having been spoiled at the point I'm writing this we still have no idea about many of the rares. I may be in the minority here but I enjoy having the commons and uncommons spoiled first with a few surprises thrown in. This produces less of a letdown than when half of a spoiler is up but the remaining cards are Draft commons. Speculation about the reprinting of shock lands also continues bolstered by the wide variety of cards that reference specific land types (Swamp Forest etc.) rather than stipulating "Basic Land."