As of writing this, about half of the cards from Ravnica Allegiance have been previewed. I mentioned on Tuesday how this can make it difficult to evaluate cards, since the context of the set is important. However, there are some cards that tend to define this context. There are similar variants of cards that are in every set. Each set has a cheap black common removal spell and expensive black common removal spell (e.g. Dead Weight and Deadly Visit). Green always has a fight spell. White always has some Pacifism variant, usually Luminous Bonds. By next week there will be enough cards to really talk about the archetypes and environment, but today there's enough to break down and evaluate some classic Limited cards in this set as well as cycles that can tell us a bit more about the format.
The hexproof common. In Dominaria we had Cold-Water Snapper, which played a very important role as a win condition and blocker. It seems as though in this set, the win-condition aspect wasn't necessary. If all you really need is a roadblock, you may very well appreciate one less mana more so than the extra two power from Cold-Water Snapper.
The developers and designers of Magic tend to be careful when it comes to hexproof. I imagine that the mana cost and size of the body were very specifically chosen. My gut says this is a hint to five as the toughness threshold of the set.
The common fight spell. In general, these spells have been good when they gave a power/toughness boost, and lackluster otherwise. Pounce was never great. Prey Upon is playable, but nothing special. Overall, I'd guess that if you're not getting the discount from Titanic Brawl, it's not going to be great. But since both green mechanics create +1/+1 counters, this may not be too difficult.
The blue bounce spell. This card can range from very good to quite bad, but I think Arrester's Admonition is likely to be on the good side. Drag Under was great last time we saw it, and Crashing Tide was a playable without the Merfolk interaction. The Ravnica Allegiance bounce spell is Drag Under if that's what you want but can also double back as instant speed interaction for combat blowouts or to just play it safe when you're ahead. I imagine the vast majority of the time you'll cast this spell at sorcery speed, but the flexibility is a nice addition.
Every format has at least one Divination at common and some have multiple. Dominaria had both Divination and Dark Bargain, so there could certainly be more to accompany Sphinx's Insight (I think it's unlikely we see more in the same category of the previous cards in this article). Sometimes formats are too fast to just do nothing but draw cards, but other formats are all about card advantage. Sphinx's Insight's role will entirely depend on whether or not Gruul and Rakdos punish taking time off to draw cards. The two-life boost or instant speed helps here, but I'm not sure it's enough. I think this card needed to either cost three mana or gain three life for it to get there. Hopefully it's still good enough, but I'm skeptical.
Green almost always gets some card similar to Overrun. Overrun is such a beating in Limited, and recently these effects have lost the trample but changed the boost to +1/+1 counters. Biogenic Upgrade places a minimum of six counters, but it can be more thanks to mechanics like adapt and riot. My gut says that six mana is just too much for this, but in the right deck it might be good enough.
There are usually one or two common counterspells, and Quench is a good one. It's pretty rare in Limited to have a counterspell that counts as a two-drop. The fact that this can always trade on curve is nice, but it doesn't scale well at all. I imagine it will be quite good and its existence will place a tax on the format where it will often be correct to play with the card in mind.
The lockets in the last format were all quite bad. They were playable in Sealed, but it was rare that I wanted to include one in my Draft deck. Occasionally you needed access to more card advantage in Dimir, or the five-color Gate deck, but it wasn't often. However, I expect both Simic Locket and Azorius Locket to have more play to them than those in the previous format. The reason for this is that both mechanics play well with Lockets.
Addendum suggests that Azorius decks will have many instants, so if you're incentivized to hold up mana frequently, the activated ability on the Locket can help hide information and is easier to activate on your gameplan. Adapt suggests that Simic will want access to lots of mana, so ramping with a Locket will have more of a home. Furthermore, adapt is something to do at instant speed, making it easier to activate a Locket without putting your guard down. The other Lockets, however, I don't expect to see much play.