To put it very generally, Genestealers are bad units right now because of how the game itself is set up. It used to be that you could leap frog from combat to combat in the Assault Phase, meaning that a Genestealer brood was protected from the first combat to what could be its third combat of a game. They die to shooting, this is obvious, but the game had a system in place to prevent shooting them and allowing their strengths to shine through. We don't have that system anymore so the unit just simply dies because of all the shooting phases it has to sit out in the open. This is further hurt by the more recent removal of their Flesh Hooks, which acted like Frag Grenades to charge through cover. Now if there's a twig in the way, the brood hits at Initiative 1 instead of the 6 you pay 14pts per model for.
Now, there are two ways to run them. One is forcing a smart play on a dumb unit, the other is just for fun and won't produce enough results to be competitive. The smart play is keeping them in a CAD for Objective Secured. Infiltrate where you can and Go to Ground with a Broodlord attached. If something comes near, activate Synapse psychic power on the Broodlord for instant removal of Go to Ground effects and charge the enemy, but that's only their secondary role. Primary role is to sit their butts down and score points on Objectives. This strategy has been done better by Space Marines Battle Company now and is FAR less effective than it used to be.
The fun way of doing things is the Manufactorum Genestealers Formation, which has some nice bonuses and meh restrictions on brood size. It's interesting, but not awesome. It does however do good in casual games, games against opponents with zero Obj Sec in their list and in Apocalypse. But Genestealers are not good at MSU. They can't survive like a Space Marine can and using the same tactics is a good way to get them killed, however, they're pointless doing anything else.
Lictors have two abilities. Perfect Deep Strike and perfect guiding for more Deep Strike. Let's say Turn 3 you need someone on Obj 6 out in nowhere 24" away from anything. Lictor comes in from Reserves right there no problem. Instant point. Or the second option, Infiltrate up close and have a Mawloc in Reserve. That Lictor is now public enemy #1 because his buddy the Mawloc won't scatter when it comes in. That's a lot of hurt on its way. The list #Lictorshame did amazingly well as an out-of-the-box way to play Nids but recent codex improvements for everyone else killed the list in the competitive meta.