Like most Tyranid players, I was not happy about losing access to the Big Rule Book powers, particularly Biomancy (even though I knew it was coming). Initially, I was very disappointed to see what I perceived as a very weak selection of psychic powers. But after spending some time considering their in-game use, I've come around a bit.
For this review, I want to run through each of the powers and their upside and down, and how I see them being used. These points will be framed around how I generally see the psyker using them, and which psyker units I think are viable.
0 - Primaris - Dominion:
This one was a tough pill to swallow at first because I was used to not worrying about synapse too much. That said, with the increased emphasis on needing to be in synapse, Dominion as a primaris becomes a reliable way to avoid much of the bad of synapse. With Zoanthropes getting a secondary roll beyond Warp Speed, you can guarantee them as 18" Synapse buffers if you need them. A single Zoanthrope is also a bit easier to keep out of the way, and a lesser tax to pay for babysitting Synapse. Additionally, in 1/6 of your games, your Warlord Flyrant will be able to use this to bump his bubble to 24", meaning even ranging out ahead, he will be keeping the front lines in synapse.
1 - Catalyst:
The immediately shining gem of the powers, Catalyst gives Feel No Pain to the caster and another unit nearby. With my babysitting Zoans, this is likely the only power that would make me reconsider taking Dominion primaris. Getting two units with FNP on one cast means a couple lucky rolls and overlapping Catalyst increases the resiliency of the army tremendously.
2 - The Horror:
This first struck me as a useless power. There are so many armies and units that are immune to pinning, so it does have limited use. That said, on a generic unit, that -2 modifier gets the unit to around a 50% failure rate. If combined with Shadows in the Warp's flat -3 Ld penalty to psykers, this could be reliably pin Warlocks, and have a decent chance of pinning a Seer Council.
3 - Onslaught:
Another power that seems to have minimal impact, but considering the short range of most of the heavy hitting guns, this can create some interesting possibilities. The biggest boost I see with this power are for Crones or Flyrants with Thorax swarms, allowing them to get closer to maximize those template weapons. The next best candidates for this power would be the Tyrannofex or Exocrine. All in all, this power makes it tougher for your opponent to premeasure to keep out of range of the most damaging weapons.
4 - Paroxysm:
I kind of skimmed over this power initially. And while not necessarily a game changer, it definitely has its uses. Decreasing the BS of a Wave Serpent or Riptide by D3 will limit its effectiveness for a turn, even with twin linked on everything.
5 - Psychic Scream:
As a 6" Nova power, this is extremely limited. Add that to the low number of wounds you're likely to cause, it seems like a pretty bad power. Honestly, I think this is the worst power of the lot. The only time I could see it being effective is against a Seer Council, who will be reduced to Ld7 because of Shadows. Even so, this power is likely to kill a single Warlock, though maybe more if you're lucky.
6 - Warp Blast:
This power didn't change much except now Hive Tyrants can use it in theory. With Zoanthropes being able to effectively cast it multiple times on a single casting roll, that's a little bit of a buff, but the short range and lack of deep strike means it will be hard to reach the best targets. Additionally, the points will often be better spent using their secondary power, for which more than a single Zoanthrope is unnecessary.