niv-mizzet wrote:
I've played them a decent amount.

Librarius and fulmination are overall good schools, technomancy and especially geokinesis are kinda crappy, save a couple powers.

Standout powers:

-veil of time is stout, though good ol' invis is better in 90% of situations.

-phase form sounds too good, but most of the time your grav centurions or whatnot can see what they want to kill anyway, so it's about the same as perfect timing. It's also in a crappy school.

-worldscape shift is neat, but easy to play around. Anyone who reads the power for more than 30 seconds should be to realize that if you hang a guy from each unit out the back of a terrain piece, and don't stand around in the open if you see an enemy assault deathstar, you neuter the power. It sounds ridic on paper, but in several games with 2 terrain pieces per 2x2 square, we've rarely found reason to cast it, as the restrictions hamper it quite a bit.

-electrodisplacement is super techy, and bonus points for coming from a good school. When combined with vicious combat deathstars, this is the only the power out of the lot that shines like a new sun. Without a deathstar to abuse it, it's still a pretty sweet strategic power that you could probably find a use for turn after turn, even if only to use it as a pseudo hit and run leaving some poor schmuck marine behind like ninjas leave behind logs.

Primaris powers are super relevant to how good a school is, so those are also worth a look:
-librarius: strong good AP small blast for wc1? Workable.
-fulmination: fire 6 heavy bolter shots for wc1? Also neat.
-technomancy: if your enemy maybe has a vehicle, and it maybe has a good shooting weapon, and is maybe facing a good direction, you can maybe shoot it...maybe. Sucky power that is situational, and even if the situation does come up, there's a random roll built into the power that will still lead to it failing half the time.
-geokinesis: a unit takes dangerous terrain and can't use armor saves against failures. This power is awful math-wise. You need to hit a dozen guys to have a 90% chance of causing a single wound, and if there are a dozen guys there, odds are the guy that gets wounded isn't very valuable. Oh, and just to make it worse, since it's a terrain test, a quarter of the game is immune to it anyway. Marine scouts, any monstrous creature, most necron decurions...anything that has move through cover. This is a pyromancy-tier fail-power.

 Runic wrote:
Take a fully kitted out wolfstar, and a Tactical Squad in a Drop Pod.

Cast Electrodisplacement on the Tactical Squad that dropped in the enemys face. Now the wolfstar is somewhere around 1-2" from the enemy on the first turn even, and can charge.

I'd say it's slightly gamebreaking.